
Class 
Book. 






CopightN?_L22i 



CQEffilGHT DEPOSIT- 



A TEXT-BOOK 



IN 



GENERAL ZOOLOGY 



BY 



GLENN W. HERRICK, B.S.A. 

PROFESSOR OF ECONOMIC ENTOMOLOGY 
CORNELL UNIVERSITY 



NEW YORK •:• CINCINNATI •:• CHICAGO 

AMERICAN BOOK COMPANY 



^ 






Copyright, 1907, 1922, by 
GLENN W. HERRICK 
Entered at Stationers' Hali^, London,, 

ZOOLOGY. 

E. P. 7 



MADE m xj. S. A. 



©CI.A677954 



MIC -9 "32 



•vu 



INTRODUCTION 

The arrangement, presentation, and selection of the subject-matter 
in the present text-book have been determined by the experience 
gained from the labors of ten years in the class room with the grade 
of students for whom this work is intended. In fact, the text is 
simply a more orderly discussion of the same subjects in the same 
sequence that have been presented for ten years to successive classes 
in elementary zoology. The author, in his work with these students, 
has attempted to interpret, with much thought and care, the zoologi- 
cal demands of such students according to their average receptivities 
and practical needs rather than by any preconceived ideas of what 
constitutes a knowledge of zoology. The aim has been to create an 
interest in nature, beget an acquaintance with the lives, habits, and 
activities of animals, train the powers of observation, quicken the 
judgment, widen the horizon of environment, augment the capabili- 
ties for independent thinking, and inculcate an unswerving regard 
for the truth. 

The instruction that a potential citizen receives in zoology must 
give more than a mere acquaintance with animals. If the study of 
this science does not accomplish the objects enumerated in the fore- 
going paragraph, it loses its highest value as an educational subject 
in the curricula of the common schools. That the study of zoology 
may fulfill its function as a subject of mental discipline and, at the 
same time, give to that large majority of pupils who become "ordinary 
citizens " an acquaintance with animals, the author has been led, from 
his experience in teaching, to include in a zoological course a goodly 
amount of natural history and comparative anatomy, a large share of 
animal ecology, economic zoology and physiology, a moderate amount 
of classification, embryology, and paleontology, something of the 
history of zoology, and, through all, a persistent presentation of the 
relationships of animals and of the manner in which they have been 
evolved. To present the foregoing divisions of the subject-matter of 
zoology in their proper relations and proportions is indeed a difficult 
task, and one which, at best, is open to criticism ; but it is hoped that 
the pupils who follow the course here laid down will gain an acquaint- 
ance with animals and acquire an interest in them, and, at the same 
time, receive that mental discipline which they would derive from 
the pursuit of other studies. 

3 



4 INTRODUCTION 

Each branch of animals has been introduced by a familiar and 
accessible type. The discussion of the type is intended (1) to express, 
in an organized form, the details of the work already supposed to 
have been done in the laboratory and field, and (2) to bring out the 
characteristics of the branch of which the type is an example. After 
the different forms of the branch have been studied, their character- 
istics are summed up, their adaptations to environment and their 
economic significance are discussed, and, lastly, a clear, concise classi- 
fication of the group is given. In the main, the classification accords 
with that given by Parker and Haswell. 

The author is greatly indebted to the following men who have read 
and criticised parts of the manuscript, covering, in most cases, their 
own special fields : Dr. Gary jST. Calkins and Dr. Henry F. Osborn of 
the American Museum of Natural History; Professors John Henry 
Comstock and G. D. Harris of Cornell University ; Dr. T. B. Palmer, 
Dr. H. F. Merriam, Dr. Leonard Stejneger, Dr. Ch. Wardell Stiles, 
and Dr. B. W. Evermann of Washington, D.C. ; Dr. J. G. Needham 
of Lake Forest University; Dr. C. Co Nutting of Iowa University; 
Professor J. S. Kingsley of Tufts College; and Mr. Edward Potts of 
Philadelphia. It is to be distinctly understood, however, that these 
men are in no way responsible for any part of the work. 

Most of the drawings were made by Miss Minnie Walker. Much 
is due to her untiring enthusiasm and devotion for the completion of 
the work. Several figures were redrawn from the " Standard Natural 
History," a few from Packard's " Zoology," with the author's permis- 
sion, several from the publications of the United States Geological 
Survey, and Figs. 143 and 235 from Jordan and Kellogg's " Animal 
Life." Figure 93 was kindly loaned by the Minnesota State Experi- 
ment Station; Fig. 201 is from a photograph by Professor H. Gar- 
man ; Figs. 110, 138, and 199 were loaned by the Cornell Nature 
Study Bureau; Figs. 99, 100, and 101 are after Snodgras ; Figs. 95, 96, 
97, and 98 were drawn by Miss Clara S. Ludlow, while a graduate 
student in biology. Figure 88 is from a photograph by Professor J. H. 
Comstock; Figs. 191 and 193 are from photographs by Dr. C. M. 
Weed; Figs. 179 and 197 are from photographs by Dr. R. W. Shu- 
feldt, while Fig. 118 is from a photograph by Mr. Victor Lowe, Gen- 
eva, New York. Figure 4 was drawn from nature by my wife, to whom 
acknowledgment is also due for information regarding the etymology 
of many words, careful criticism of the manuscript, and helpful sugges- 
tions concerning the subject-matter. The remainder of the photo- 
graphs, drawings, and diagrams are by the author. 

GLENN W. HERRICK. 



CONTENTS 



I. 

II. 

in. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 
X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

XXI. 

XXII. 

XXIII. 



The Relation of Animals to Minerals, to Plants 
and to One Another 

The Nature of the Cells of which Animals 
and Plants are Composed .... 

The Growth of Animals and the Functions of 
their Organs 

The Classification of Animals 

Amceba, A'orticella, Paramecium . 

Sponges 



IIydr.e, Jellyfishes, Sea Anemones, Coral Polyps 
Flatworms, Roundworms, and. Rotifers 
Earthworms, Leeches, and Seaworms . 
Starfish, Sea Urchin, Brittle Stars . 
Mussels, Clams, Oysters, Snails, Squids 
Clams, Oysters, and Mussels .... 
Crayfish, Lobsters, Spiders, and Insects . 
Scorpions, Spiders, and Ticks 

Insects 

Other Members of the Class — Insecta 

Branch XII. — Chord ata 

Urociiorda and Vertebrata . 

Fishes , 

Frogs, Toads, and Salamanders , 
Snakes, Turtles, Lizards, Crocodiles . 

Birds 

Birds (Continued) 



11 

18 

24 

29 

36 

45 

64 

75 

89 

103 

112 

124 

144 

155 

170 

200 

203 

208 

229 

246 

268 

279 



CONTENTS 



PAGE 

XXIV. Mammals 302 

XXV. Mammals (Continued) ...... 311 

XXVI. Animals of the Past 341 

XXVII. The Struggle for Existence . . . . 353 

XXVIII. Life Processes of Animals 360 

XXIX. The Geographical Distribution of Animals . 366 

XXX. The History of the Science of Zoology . 374 

Index 381 



ZOOLOGY 

I. THE RELATION OF ANIMALS TO MINERALS, 
TO PLANTS, AND TO ONE ANOTHER 

Most of us are familiar in a general way with animals 
and plants, and with those inanimate objects we call 
minerals. Yet not all of us, if asked suddenly, could tell 
the difference between an animal and a piece of coal. It 
would hardly do to say that the difference lies in the ability 
of an animal to move from place to place while the piece 
of coal cannot, because some animals cannot move about 
any more than the coal ; for example, sponges, coral polyps, 
etc. Moreover, there is a similarity between an animal and 
a piece of coal of which we had perhaps never thought. 
Either of them, if subjected to high heat for a sufficient 
length of time, will be reduced to ashes. Since the ashes 
to which plants and animals are reduced by heat con- 
sist of mineral matters, it is evident that these organisms 
are built up, partly at least, of mineral substances and to 
this extent are similar to coal. 

This structural relation of plants and animals to minerals 
is much more intimate than we are accustomed to think. 
Plants take up mineral substances, — carbon, hydrogen, 
and oxygen, — form starch from them, and use that starch 
as food to build up vegetable tissue. Animals depend 
largely for their food upon the starch and cellulose manu- 
factured and stored up by plants. Evidently, then, animals 

7 



8 



ANIMALS, MINERALS, AND PLANTS 



are dependent for their very existence upon inorganic sub- 
stances, and ultimately, when life is extinct, they are re- 
duced to the same inorganic mineral materials from whence 
they sprung. 

Notwithstanding the dependence of animals upon min- 
erals, there is unquestionably a great difference between 

them. This difference 
resides largely in the fact 
that animals possess that 
subtle and indefinable 
characteristic called life, 
while minerals do not. 
On the other hand, the 
difference 'that exists be- 
tween animals and min- 
erals does not exist 
between animals and 
plants; for both of the 
latter possess life and 
hence are evidently much 
more closely related to 
each other than to min- 
erals. In fact, so closely 
do animals and plants 
resemble each other in some cases, that it is often im- 
possible to tell them apart. For example, look at the 
animal and the plant shown in Figure 1, and note the 
impossibility of deciding from appearances which is an 
animal and which is a plant. It is easy enough to 
tell a horse from a tree, but as we go lower in the 
scale of life, animals and plants become more and more 
alike in appearance. In fact, it is impossible to give a 




Fig. 1. — A, Gorgonia; C, Fucus. 



ANIMALS, MINERALS, AND PLANTS 9 

definition which will include all animals and exclude all 
plants, and vice versa. If it is said that animals move, we 
may reply that many plants, especially certain aquatic 
plants, move as freely as animals. If it is said that animals 
have sensibility, we may reply that plants show the same 
characteristic. If it is said that plants have a green color- 
ing matter, chlorophyll, we may point to the same sub- 
stance found in the bodies of certain fresh-water hydras. 
If it be maintained that animals take up oxygen and give 
off carbon dioxide, we can demonstrate that plants do pre- 
cisely the same thing. There is, however, one character- 
istic common to all plants and all animals ; namely, the 
possession of life. 

Whether we deal with plants or animals, then, we shall be 
in constant contact with life and yet probably never be 
able to tell exactly what it is. We can, nevertheless, find 
out something of the attributes and characteristics of life, 
and that will be our aim in the following pages. 

Zoology. — By separating the term zoology into its 
parts, we find it is made up of two Greek words; namely, 
zoon — animal, and logos — discourse. Therefore, Zool- 
ogy may very properly be termed a discourse on the habits, 
structures, development, and functions of animals. 

Zoology, along with chemistry and physics, is one of the 
most extensive of all the sciences. The species of animals 
upon the earth are myriad in number. It is estimated 
that there are over a million species of insects alone, of 
which over three hundred thousand have actually been 
studied and named. 

Among so vast a number of animals, many forms are met 
that are apparently unlike in every way. Yet each animal 
which we shall study or which we may find upon the earth 



10 



ANIMALS, MINERALS, AND PLANTS 



$ytll^h*t*viMn*"S'*'t 






is like every other animal in one respect ; each begins 

as one cell and, when mature, is made up of either one cell 

:• .'.••.>..••. .*.«,-. , ••• (-^&- 2), or a combination of many 

;i:J:i;i^:^ :: jjj:-! cells, together with the substances 

;!:;;•: -ifeS':^ <Z lying between, which connect the 

cells and hold them together. For 
example, one of the simplest ani- 
mals, the amoeba, is composed of 
but one cell, during its whole life. 
On the other hand, the whale is 
made up of millions of cells, to- 
gether with the substances which he 
between the cells and hold them in 
place. The one cell of the amoeba 
71 performs all the functions of life, 
i.e. assimilation, reproduction, res- 
piration, growth, etc. ; while in the 
body of the whale, these functions 
are distributed among groups of 
^ cells, each group having; its own 

Fig. 2. — Cell of epithelial ; ' • r 

tissue; a, cilia; n, nucleus. Special lunctlOn to perioral. 



:m? 



§i-~ 



MM 



m 



[I. THE NATURE OF THE CELLS OF WHICH 
ANIMALS AND PLANTS ARE COMPOSED 

A cell. — Most of us, no doubt, think of a cell as a space 
inclosed by walls, for example, a crayon box. In zoology, 
however, we must learn to think of a cell as something 
quite different from the above. In fact, a living plant or 
animal cell, instead of being simply a walled-in cavity, 
is a minute portion of semifluid substance known as pro- 
toplasm, which may or may not be inclosed by a wall. 

A plant cell. — Since animal and plant cells are so much 
alike, and since it is easier to see plant cells, we shall 
examine these first. A melon vine or squash vine is covered 
with a multitude of small white hairs. Each of the hairs 
(Fig. 3, A), when examined under the microscope, is found 
to be a slender, cylindrical filament, cut up by cross walls 
into several distinct divisions. Each of these divisions 
is a cell, and each cell is bounded by a thin, transparent 
wall. The wall, therefore, forms a delicate sac within 
which is an almost colorless, granular liquid called proto- 
plasm. The granules may be seen to flow along definite 
threads or streams (Fig. 3, B) in the cell by which we con- 
clude that the protoplasm has a streaming movement. 
Protoplasm, in its simplest form, appears to be of the 
same structure throughout and somewhat resembles the 
white of an egg. Actually, it is a very complex substance 
incapable (in the living state) of chemical analysis. Usu- 
ally, as seen in animals and plants, it is granular. In 

11 



12 



NATURE OF CELLS 



if:^ 



■--^~sp. 



--71 



every vitally active plant and animal cell, this granular 
liquid protoplasm is found. It is the essence of life and is 

a wonderful substance. It 
/ makes new flesh, blood, and 

bone. In fact, protoplasm 
does everything that is ac- 
complished in an animal or 
plant. 

In a living cell, the proto- 
plasm is not of the same 
structure throughout ; some 
parts of it differing greatly 
in structure and function 
from other parts. For ex- 
ample, a small, well-defined 
spot may be seen, usually 
along one side of the cell of 
the melon hair, about mid- 
way of its length. This is 
an organized structure of the 
protoplasm known as the 
nucleus. The remainder of 
the protoplasm in the cell 
is much thinner than the 
nucleus, has a different func- 
tion to perform, and is 
known as cytoplasm. The 
streams of cytoplasm seem 
to run toward the nucleus or 
away from it. In other words they all seem to begin and 
end there. Even without other evidence this would show 
that the nucleus must be very important. It is plain that 



Fig. 3. — A, hair of melon vine, show- 
ing cells ; B, cell much enlarged ; sp, 
streams of protoplasm ; n, nucleus. 



NATURE OF CELLS 13 

if the cytoplasm is confined to the streams noted, it does 
not completely fill the cell. The spaces between the 
streams are filled with a watery fluid known as sap, or 
more properly as cell sap. We must not get the idea from 
this hair cell that all plant cells have walls about them, for 
they do not. Certain low plants consist, most of their 
lives, of a mass of free, nucleated protoplasm not con- 
fined by walls, but creeping about under decaying logs, 
leaves, etc. 

Animal cell. — It is rather difficult to find an animal cell 
in which we can see the protoplasm as plainly as in the 

melon hair, with- 
er? 

out spending con- ....... JaL / 

siderable time and -' - , -- Js^ / .^ 

labor in staining, ,\ '^V'"'"^® 

sectioning, etc. ;; # ■* • \jL'^r£< m 

But the amoeba, a Y"'^ ff -e _ * _.?" 

.-■ij.iV;.j:v>':>;-.'. 1 ;- j~.- .:.■?•.• 

veiy simple animal / ^^' " " l $£ .*. n 

found in the mud / '-ov*-' :'-W-fc ' J 

and ooze of ponds / y' ^Sfe-_ rj 

and ditches, affords fy_'_ '"©■£ '**-., * 

an example of an pS 

animal Cell that Fig. 4. — Amoeba, enlarged ; cv, contractile vacu- 

can be easily ex- ole ;. fv > f ° od ™™ ole '> n > nucleu f '> ps ' P seudo " 

J podia ; end, endoplasm ; ect, ectoplasm. 

amined. It is so 

small and simple that one cell forms the whole animal, 
and hence, a study of the amoeba (Fig. 4) constitutes a 
study of an animal cell. 

Where the amoeba is found. — Living in the ooze and 
slime on the leaves and sticks in ponds, ditches, and streams, 
are found many kinds of microscopic animals. It is in 
such situations and in such company that the amoeba is 



14 NATURE OE CELLS 

found. It exists wherever such bodies of water are found, 
and, with care, may be obtained for study. 

Structure of the body. — The body of the amoeba is simply 
a minute mass of semiliquid, colorless protoplasm that 
has no permanent form because it is constantly changing 
in outline and shape. It may contract into a tiny ball, 
or it may become star-shaped, or it may stretch out 
and become very thin. 

The protoplasm of the body is granular in structure, is 
not confined by a wall, and is differentiated into two 
distinct parts, the nucleus and cytoplasm. The nucleus is 
a light, roundish spot, usually somewhere near the center 
of the body. The remaining part of the protoplasmic 
mass, surrounding the nucleus and composing nearly the 
whole of the body, is the cytoplasm. The outer layer of 
the cytoplasm is somewhat denser and more transparent 
than the inner part. This bounding layer is called the 
ectoplasm, while the inner, granular part of the cytoplasm 
is called the endoplasm. 

While the body of the amoeba is active, slender, finger- 
like processes of the protoplasm, called pseudopodia (Fig. 4), 
slowly stream out from the body mass as though they were 
feelers seeking the way. These pseudopodia are often ex- 
tended and withdrawn without a change in position of the 
body of the amoeba. Not far from the nucleus is a trans- 
parent body, which, if watched long enough, will be seen to 
enlarge slowly and then to discharge its contents suddenly 
into the surrounding water. This is the contractile vacuole. 

Method of locomotion. — The amoeba has no wings or 
legs, yet, by watching it closely, it will be found to change 
its position slowly, and in this way. One side of the body 
begins to bulge out, and this projection soon develops into 



NATURE OF CELLS 



15 



a pseudopodium. The entire substance of the amoeba then 
slowly streams forward upon this false foot. Another 
pseudopodium is put out, the streaming movement of the 
body takes place again, and by a succession of these move- 
ments, the amoeba creeps about from place to place. 

Manner of obtaining food and digestion. — Whenever a 
pseudopodium or any part of the body comes in contact 
with a desirable bit of food, the latter is gradually sur- 
rounded and ingulfed, as it were, by the body mass (Fig. 5). 
The ingested bit of plant is then gradually digested and 







Fig. 5. — Series of diagrams showing an amoeba eating a minute plant. 
After Verworn. 

made a part of the protoplasmic mass, that is, assimilated. 
The amceba has no stomach or special organs of digestion, 
but any part of the body can take in and digest the food. 
The particles of ingested food are usually surrounded by 
a layer of water that is taken in at the same time. Gener- 
ally several of these balls of food with their enveloping films 
of water may be seen in the body. They are called the 
food vacuoles. 

Elimination of waste matters. — The solid, undigested 
portions of the food are thrust out of the body into the water 
through temporary openings in the ectoplasm. These parti- 
cles of solid matter are usually eliminated from that portion 
of the protoplasm in the rear part of the moving animal. 



16 NATUKE OF CELLS 

The contractile vacuole is an organ of excretion and aids 
in getting rid of the waste matter of the body. Carbonic 
acid gas, water, etc., pass out directly through any part of 
the surface of the body into the surrounding water. In 
other words, the excretion of waste products may go on 
anywhere over the surface of the body. 

How the amoeba breathes. — This animal is surrounded 
by water containing oxygen, and this gas is taken into the 
body of the amoeba through any part of its surface. Vice 
versa, carbonic acid gas is given off from any part of the 
body. It is probable that the pseudopodia are formed 
partly to increase the surface of the body in order to 
facilitate respiration. 

Reproduction of the amoeba. — When a new amoeba is 
to be produced, all the pseudopodia are withdrawn and the 
animal lies quiet for a time. Finally, the nucleus begins 
to divide in half, and at the same time a constriction ap- 
pears around the middle of the body. The nucleus finally 
divides in two; but while it is doing so, the constriction 
around the body becomes deeper and deeper, until finally 
the body is cut in two parts, each part with a half of the 
original nucleus (Fig. 6). Each part with its nucleus is 
really a new amoeba. This is the simplest method of 
reproduction known and is called fission. 

Sensation in the amoeba. — When the amoeba comes in 
contact with a bit of food, it reacts toward the food, and 
when it touches a grain of sand it moves out of the way; 
hence this primitive animal evidently possesses sensation. 

Animal cells in general. — As a rule, animal cells have 
no well-defined walls about them, and for this reason the 
term cell is a misleading one. The cell has been called 
the unit of structure in an animal because animal tissues 



NATURE OF CELLS 



17 



are made up of an aggregation of cells, — nucleated masses 
of protoplasm. In the many-celled animals, the cells are 
of various shapes and have various functions to perform. 
Some cells are cylindrical, some spherical, some flat and 
scalelike, some like a cube, some like a pyramid, and some 




Y 



biG. 6. — Stages in the division of an amoeba. After Schultze. 

greatly elongated and spindle-shaped. Some cells perform 
the function of motion, e.g. those of the muscles; others 
carry impulses, e.g. the nerve cells; others secrete digestive 
fluids, e.g. those of the salivary glands. To sum up, then, 
a living animal cell may he defined as a mass of living yro- 
toplasm with a nucleus and usually without a definite wall. 

jjekrick's ZOOl, —2 



III. THE GROWTH OF ANIMALS AND THE 
FUNCTIONS OF THEIR ORGANS 

Spontaneous generation. — A jar of water containing a 
handful of hay will literally swarm with microscopic ani- 
mals at the end of a week if left standing in a warm room. 
Apparently these animals arise spontaneously or spring, 
as it were, from nothing in the way of animal life. Formerly 
zoologists called this sudden appearance of so many active 
animals a case of spontaneous generation. 

Ancient zoologists held that flies were spontaneously 
generated in the flesh of dead animals; and that frogs, 
toads, and reptiles might be produced from the moist, slimy 
earth of rivers and seas. We now know that flies, frogs, 
and toads develop from eggs deposited in favorable places 
by the female parents. And Pasteur has shown that when 
infusions of hay are boiled and hermetically sealed they may 
be kept indefinitely without a trace of animal life. More- 
over, it has been demonstrated that many plants and ani- 
mals produce great numbers of tiny cells known as spores 
or germs, and that these fall upon grass and in the water. 
Therefore, when these two substances are put together in a 
suitable temperature, the spores germinate and produce 
swarms of minute animals; but if the spores are killed by 
boiling, no animals appear in the infusion. It would seem, 
then, that there is no such thing as spontaneous generation, 
but that all life comes from some life that went before. 

18 



THE GROWTH OF ANIMALS 19 

How animals begin. — Every animal, 1 no matter how 
large or how small, begins as one cell, and in this all ani- 
mals are alike. 

This one cell, in the majority of animals, is known as 
the egg cell, or ovum. The egg cell itself is very small; 
but in many cases, especially in the case of those animals 
that lay eggs, the egg cell is inclosed in an enveloping mem- 
brane, which in turn may be inclosed in a hard, thick shell. 
The membrane and shell have within them, in addition 
to the egg cell, a considerable quantity of food, known as 
the yolk. The egg cell, with its food yolk and membrane 
and shell (when the latter is present), constitutes what we 
know as an egg. Eggs vary greatly in size, owing to the 
difference in the quantity of food yolk they contain. For 
example, a hen's egg is much larger than the egg of a pond 
snail, because the former contains much more food than 
the latter. 

The majority of animals lay eggs, sometimes on land (e.g. 
bird, turtle, etc.), sometimes in water (e.g. fish, frog, etc.), 
but sometimes the eggs are retained in the body of the 
parent animal. Moreover, most of the mammals retain 
the egg cell and allow it to develop into an embryonic ani- 
mal within the body of the mother. But whether the egg 
cell is deposited outside of the body of the mother, or 
whether it is retained within the body of the mother for a 
certain period, it undergoes similar changes in its develop- 
ment into an adult animal. 

How cells increase in number. — We have learned in the 
foregoing paragraph that all animals begin as one celL Yet 
the animals with which we are most familiar consist of 

1 This may not hold strictly true in case of the hydra when it 
reproduces by budding. 



20 



THE GROWTH OF ANIMALS 



myriads of cells. Consequently, the one cell with which 
they began has been increased in number many times. 
The manner in which the cells in an animal's body in- 
crease in number is important and interesting. 

Perhaps the simplest manner in which cells may increase 
in number is shown by the amoeba. We have seen that a 

new amoeba is formed 
simply by division, or 
fission of the body. 
In this process of the 
formation of new 
cells, no remarkable 
changes occur. But 
in the case of higher 
animals, when a cell 
divides, the nucleus 
usually passes through 
a remarkable and 
complicated series of 
changes to which the 
term karyokinesis, or 
mitosis, is applied 
(Fig. 7). A spindle- 
shaped body with a 
starlike organ at each 
end forms in the cell. 
The substance of 
the nucleus, which 
has meanwhile been 
transformed to rodlike bodies called chromosomes, is then 
drawn to the spindle. Finally, each of the chromosomes 
splits in two equal parts, and one half of the resultant 




Fig. 7. 



■ Stages of cell division by mitosis. 
Diagrammatic. 



THE GROWTH OF ANIMALS 21 

number then passes to one end of the spindle and the 
other half to the opposite end of the spindle. The spindle 
then contracts in the middle and eventually breaks in 
two, as it were, and after a few more changes two com- 
plete new nuclei are formed, after which the body of the 
cell divides in two, thus forming two new cells. Figure 7 
shows these changes in detail. 

Growth of animals. — Growth takes place in an animal 
mainly by an increase in the number and size of the cells. 
This means, in general, that a tiny kitten does not possess 
as many cells as a large kitten and that a large kitten does 
not possess as many cells as a full-grown cat. 

Before the egg cell, from which most animals originate, 
begins to form mother cells, it must be fertilized by the 
male sperm cell. After fertilization it is known as the 
fertilized egg cell, or oosperm. The oosperm may begin at 
once to divide and start the development of the animal. 
The character of the division varies in different cases, but, 
in general, the oosperm, or a part of it, divides into two cells, 
these into four, these into eight, these into sixteen, and so on 
until a globular ball of similar cells is formed. At this point 
in the development of the embryo, a change occurs and the 
cells cease dividing so regularly in multiples of two. They 
now begin to differ from each other in shape, size, and func- 
tion, and some of them go to form skin, others to make bone, 
others to build up muscles, and so on until every part of the 
animal is formed. While this activity among the cells is 
going on, food is needed to furnish energy and materials 
out of which the cells may be built. Even after the animal 
is formed, a constant supply of food is demanded for build- 
ing new cells to take the places of those worn out and cast 
off. 



22 



THE GROWTH OF ANIMALS 



Organs of animals. — The body of an ox is made up of 
many different parts, or organs, and each organ has a certain 
function, or work, to perform. For example, the lungs per- 
form the function of purifying the blood, the legs are for 
locomotion, the ears for hearing, and the eyes for seeing. 
We may define an organ, then, as a part of an animal that 
has some definite function to perform. 

The relation of function to structure. — The leg of a duck 
performs the double function of walking and swimming. 




Fig. 8. — Foot of duck, blue jay, mole, and seal, respectively, showing 

adaptation to function. 

It is accordingly provided with joints, muscles, toes, and a 
web between the toes. The feet of a blue jay are fitted for 
perching. The limbs of a seal are fashioned for swimming 
and the feet of a mole for digging (Fig. 8). The teeth of a 
dog are constructed for tearing flesh, but the teeth of an 
elephant are suited to grinding vegetable material. From 
these examples, it will be seen that the structure of an or- 
gan is suited to the work, or function, it has to perform. 
The higher we go in the scale of animal life, the more com- 
plex becomes the function and structure of organs. This 
is shown by the fact that a bird's wings are much more 



THE GROWTH OF ANIMALS 23 

complicated, both in structure and in the work that they 
do, than the fore legs of a grasshopper. 

The animal as a machine. — We have seen that the body 
of an animal is made up of many parts, or organs, each with 
its own particular work, or function, to perform. With 
respect to its structure, then, an animal's body is very similar 
to a machine. In truth, the animal body may be considered 
a machine, in which each part performs a special kind of 
work, and although dependent on the other parts, con- 
tributes its share to the labor of the machine as a whole. 
For example, a locomotive has a fire box into which the 
fuel is thrown that is to produce the energy to run the 
engine. Similarly, the animal body has an alimentary 
canal which receives and assimilates the food from which 
energy is derived. The locomotive is provided with a 
smokestack and exhaust valves to conduct away the waste 
materials, while the lungs, skin, and kidneys act in a similar 
capacity for the body. The engine has its steam cylinders 
in which the transformed energy of the fuel, through the 
medium of steam, sets up motion. In a corresponding 
manner, the animal body is furnished with muscles, through 
which the transformed energy of the food expresses itself 
in the form of motion. Moreover, the engine must be sup- 
plied with fuel and water to keep it running; and similarly 
the animal body demands food and water to maintain its 
activity. If the steam cylinders of the engine wear out, 
the locomotive becomes useless. If the kidneys of the 
animal body become incurably diseased, the body dies. 

Of course, it must be remembered that the animal body 
has that subtle and indefinable characteristic we call fife 
which the locomotive has not; and this makes a very 
great and real difference between them. 



IV. THE CLASSIFICATION OF ANIMALS 

In most libraries, the books are arranged on the shelves 
in a certain order. One class of books occupies a certain 
shelf or shelves, and another class, other shelves. Or, as 
we say, they are classified and arranged. For example, 
all books of history are put into a group by themselves, 
books of fiction into a group by themselves, books of biog- 
raphy by themselves, and so on through the list. 

Now in much the same way animals are gathered together 
in groups. Certain ones much alike are put into one group, 
certain others much alike but differing from those in the 
first group are put into another group, and so on through 
the whole animal kingdom. Like the books in the librae, 
animals are arranged in groups for convenience of study. 
More than this, however, animals are gathered into groups 
that we may get a better understanding of their relation- 
ships to each other. In our study of animals we shall find 
that a relationship, 1 or kinship, exists throughout the 
animal kingdom from the amoeba to man. Each animal 
bears a certain relation to the remaining members of the 
kingdom, although this relation is much closer with some 
animals than it is with others. The object of zoological 
classification is to express the relation of one animal to 
the others in the kingdom and to determine what place it 
occupies in the great assemblage of animals. The classi- 

1 By this we do not mean that the members of the animal kingdom 
form a serial arrangement, but rather such an arrangement as is 
shown by the diagram in Figure 9. 



THE CLASSIFICATION OF ANIMALS 25 

fication of animals is a most fascinating study and one 
that trains the mind, develops the powers of observation 
and discrimination, and strengthens the judgment. 

If we were to attempt to classify animals according to 
color, we should have some buffaloes, some cats, some 
monkeys, and some birds in one group. Plainly this would 
be a poor classification and of no use. The groups into 
which animals are gathered are based upon permanent 
anatomical structures or fixed characters rather than upon 
superficial resemblances. These groups are of different 
rank and vary greatly in size, for the groups of high rank 
contain or include many more animals than those of low 
rank. 

Species. — The smallest and lowest group which is usually 
taken into consideration is that known as species. For 
example, we know that all of the common house cats 
have claws alike, possess the same kind of eyes, make a 
similar purring noise, and are of about the same size when 
full grown. Consequently, we consider them the same 
kind, or species of animals. Moreover, all house cats, of 
whatever size or color, belong to the same species. Fur- 
thermore, we know that kittens will grow and become like 
their parents. Therefore, we may, in general, consider a 
species as a collection of animals, the individuals of which 
possess several similar, fixed, and permanent characters 
and the offspring of which possess the same unchanging 
characteristics. 

Genus. — If a cat be compared with a tiger, many points 
of resemblance between the two animals will be noted. 
Both have long, slender, agile bodies, the same noiseless 
tread, much the same kind of mouth with long bristles on 
each side of the upper lip, and similar eyes. On the other 



26 THE CLASSIFICATION OF ANIMALS 

hand, the tiger is much larger and stronger, its body is 
differently marked, and the fur is more compact and glossy. 
It is evident that these two animals are of a different kind, 
or species, yet are very closely connected. In fact, they are 
so closely related that they are placed in one and the same 
group known as a genus. Again, the lion and the leopard 
are two distinct species of animals, but so closely related 
to each other and to the tiger and domestic cat that they 
are included in the same genus. A genus usually in- 
cludes several closely related species, but it may consist 
of one species only. 

How animals are named. — The scientific name of each 
animal consists of two words taken from the Latin or Greek 
languages, usually the former. The first word of the name 
is the name of the genus to which the animal belongs. 
The second word is the name of the species to which the 
animal belongs. For example, the scientific name of the 
domestic cat is Felis domestica, in which Felis indicates the 
genus and domestica the species to which the cat belongs. 
In like manner the lion is known as Felis leo, the tiger as 
Felis tigris, and the leopard as Felis pardus. This method 
of naming animals tends to insure uniformity, because every 
zoologist, no matter of what nationality, in writing of a 
particular animal, uses the same name, thereby avoiding' 
confusion and, at the same time, indicating the precise 
animal under discussion. 

Family. — If a wild cat and Canada lynx were compared 
with a tiger and a house cat, we should find that they pos- 
sessed similar eyes, walked in a similar manner, and had 
similar mouths with whiskers on the upper lips. It is 
evident that they are all catlike animals. On the other 
hand, we should find that the lynx and wild cat differed 



THE CLASSIFICATION OF ANIMALS 27 

from the house cat and tiger by possessing triangular ears, 
short tails, and comparatively long legs. Moreover, the 
lynx has a pencil, or tuft of hairs on each ear, and occasion- 
ally a wild cat is found with ears bearing like tufts. Plainly, 
the lynx and wild cat differ enough from the tiger and 
domestic cat to be considered different species. In fact, 
the differences between them are so great that the lynx and 
wild cat are placed in a different genus from that to which 
the tiger and house cat belong. Therefore, the lynx and 
wild cat represent one genus, while the cat and tiger rep- 
resent another and different genus. But, since they are 
all so catlike, they, together with the leopard, lion, panther, 
jaguar, etc., are placed in a group known as a family (cat 
family). In like manner, the dogs, wolves, foxes, etc., 
form the dog family. 

Order. — To go further, we know that the house cat, tiger, 
lion, lynx, dog, fox, wolf, bear, and raccoon resemble one 
another in possessing teeth fitted for tearing and eating 
flesh, which forms all or a greater part of their food. There- 
fore, all of these animals are assembled together in one 
large group known as an order (Carnivora). 

Class. — Again, the bears, dogs, cats, tigers, lions, wolves, 
etc., resemble buffaloes, elephants, deer, rats, mice, etc., in 
possessing milk glands and suckling their young. There- 
fore, all of these animals are gathered together in a group 
known as a class (Mammals). 

Branch. — Finally, all of the foregoing animals, together 
with birds, fishes, reptiles, etc., possess, at some time of 
their life, a semicartilaginous cord that runs along the 
back between the nervous system and the alimentary canal, 
known as the notochord. Therefore they are all placed in 
one group known as a branch (Chordata). 



28 



THE CLASSIFICATION OF ANIMALS 



To put all this in a simpler form, we would say that indi- 
viduals are grouped together to form species, species to 
form a genus, genera to form a family, families to form an 
order, orders to form a class, and classes to form a branch. 

The following table illustrates the classification of the 
domestic cat: 

Kingdom, Animalia. All animals. 
Branch, Chordata. Having a notochord. 

Class, Mammalia. Having milk glands and suckling young. 
Order, Carnivora. Eating flesh. 

Family, Felidce. Having sharp, retractile claws. 
Genus, Felis. Cat, lion, tiger, leopard, etc. 
Species, Felis domestica. Domestic cat. 

As we said before, in our 
study of animals we shall find 
a kinship existing throughout 
the animal kingdom. More 
than that, we shall also find 
a step-by-step progress from 
the lowest to the highest. 
This very important point 
will be brought out more 
clearly farther along, but can 
best be represented here by a 
tree diagram. By the latest 
authority, the animal king- 
dom is divided into twelve 
great branches; but for the 
sake of simplicity we have 
grouped four of these into 
one — the worms — in the 
diagram (Fig. 9). 




Fig. 9. — Diagram illustrating 
classification. 



V. AMCEBA, VORTICELLA, PARAMECIUM 

Branch I. — Protozoa (protos, first; zoon, animal) 

All of the protozoans are very simple in structure, for all 
are single-celled animals. Frequently, the cell composing 
■the body of a protozoan possesses a wall, but sometimes it 
does not. One point in regard to these animals is of especial 
interest; namely, that all the processes of life are carried 
on by this one cell. Every member of this group has the 
power of motion, digestion, assimilation, and reproduction, 
all of which functions are necessarily performed by the 
one cell. They are mostly microscopic and are widely dis- 
tributed. Some live in salt water, and some live in fresh 
water. 

An Example of the Branch — the Amceba 

We have already fully discussed the amceba in a former 
chapter, and shall, therefore, pass directly to a considera- 
tion of other members of the Protozoa. 

Protozoans with shells. — The amoeba has no shell, not 
even a cell wall for protection. But there are many proto- 
zoans that possess shells. Some of the shells are com- 
posed of carbonate of lime, some are made from silica, 
while some are formed from grains of sand cemented 
together. Most of the shelled protozoans are marine; a 
few are found in fresh water. The marine species are 
found at various depths in the sea. Some of them live at 
or near the surface of the ocean, and others live at great 
depths. 

29 



30 AMCEBA, VORTICELLA, PARAMECIUM 

One great group, or order, called Foraminifera, are nearly 
all marine. The shells of these animals, in most species 
composed of lime carbonate, have either one or two large 
terminal openings or are perforated with many minute 
openings. Through these minute holes there project long, 

delicate protoplasmic threads, the 

; | J J / ;j /;// pseudopodia. These fine pseudo- 

* \\ ll ' /// lii/ si; '' V°di& often unite to form a net- 

-^|^v!|i \l ji£>0^ work about the shell (Fig. 10). 

'^^^^^Ji^^^^'-.-' The shells of many Foraminifera 

^^^K PIP"'"'" --" are ra ^ ner complicated in struc- 

_.,__j|b - . ture and present a variety of 

W 1 ^V>~ shapes and patterns. Many of 

^^^^^fe?-.: them are divided into chambers. 

V ^\V; \ Nevertheless, they are one-celled 

Fig. 10.— One of the Forami- animals, because all the chambers 

nifera with streams of proto- CO nnected with one another 

plasm (pseudopodia) project- 
ing through openings in the so that the protoplasm consti- 

shell. After Schultze. tuteg Qne body ^^ Qr ^ 

The marine Protozoa are myriad in number of individuals. 
One species especially, called Globigerina, lives in such 
immense numbers in the sea, usually near the surface of the 
water, that the dead shells, which are constantly falling 
downward, form a mud, or ooze, in some cases of consider- 
able thickness, on the bottom of the ocean. The shells of 
this animal are microscopic in size, and composed of lime 
carbonate. In England and France, great beds of white 
chalk exist to-day which, when examined under a mi- 
croscope, prove to be composed almost wholly of the shells 
of globigerina and other minute Foraminifera. 

Slipper animalcule, or Paramecium. — Unlike the amoeba, 
this protozoan has a definite shape. It is microscopic, but 



AMCEBA, VORTICELLA, PARAMECIUM 



31 



just on the border of vision, and is shaped somewhat like a 
slipper. It may be obtained in abundance from an infusion 
of hay. 

The body of the slipper animalcule is inclosed with a thin 
cuticle which retains the shape of the body. All over the 
body are longitudinal rows of minute, eyelashlike appen- 
dages, called cilia. The Paramecium moves swiftly through 
the water by means of the rapid vibrations of cilia. On 
account of their rapid motion, the cilia are difficult to see in 
a living specimen. 

On one side of the body is a long, slightly twisted groove 
(Fig. 11), known as the oral groove, that extends into the 





Fig. 11. — Slipper animalcule much enlarged; m, mouth; g, gullet; 
w, waste matter; fv, food vacuoles; cv, contractile vesicles; n, large 
nucleus. 

body and finally becomes a tube. At the beginning of 
this tube is the mouth. The Paramecium has two con- 
tractile vacuoles, one near each end of the body. Two 
nuclei are present, but difficult to see. 

Paramecia reproduce by fission in much the same man- 
ner as the amoeba. There comes a time, however, when it 
seems that the process of fission cannot be repeated again 
until quite a different process has taken place. This pro- 
cess is known as conjugation and may be considered a re- 
juvenating process. Two individuals come together, and 
an actual interchange of a part of the substance of the 



h < hi 
32 AMCEBA, VORTICELLA, PARAMECIUM 

nucleus of each animal takes place. After conjugation 
occurs they reproduce rapidly by fission as before. 

Bell animalcule, or vorticella. — These animals occur in 
infusions of hay and in bodies of fresh water attached to 

leaves, sticks, and pond 
scums. The body is 
shaped like an inverted 
bell and has a long, 
slender stalk by which 
it is fastened to objects 
in the water. The body 
is invested with a trans- 
parent cuticle, but the 
cilia are confined to the 
edges of the bell and 
vestibule. On the mar- 
gin of the bell is a deep 
oral groove, the vestibule, 
that extends downward 
toward the center of the 
body (Fig. 12) and ends 
with the mouth. The 
long, slender stem is 
composed of an outer 
transparent sheath and 
an inner muscular rod, 
or axis. In nature, these 




Fig. 12. — Bell animalcule, or vorticella: 
e, gullet ; n, nucleus ; cv, contractile vacu- 
ole ; a, axis ; s, sheath ; fv, food vacuole. 



little animals are constantly pushing out and darting back 
to their places of support by means of the uncoiling and 
coiling of the slender stems. As one darts back, the edges 
of the bell become inverted and turned inward so far that 
the body assumes a globular shape. As it slowly pushes 



AMCEBA, VORTICELLA, PARAMECIUM 33 

out again, the edges turn outward and the body expands 
until it gradually assumes its former shape. 

Vorticella? reproduce by fission, one of the resultant forms 
swimming away and developing a stalk for attachment. 
At times they conjugate, while some individuals may 
become encysted and divide up into spores or germs 
which finally escape from the cyst and develop into new 
individuals. 

General characteristics of the Protozoa. — With the 
amoeba, we started among the most primitive animals. It 
may seem strange that the oldest animals are the simplest, 
but it is true. It is probably due to the fact that these 
animals have always lived in the water, and the water is 
probably not very different to-day from what it was ages 
ago. Hence there has been nothing to bring about change 
in these animals, and they have remained much the same. 

Again, bear in mind that we have been dealing entirely 
with one-celled animals. Yet they can do, in a simple, 
primitive way, much that we can do. They can all move; 
some slowly,, by crawling, as the amoeba; some faster, 
by thousands of cilia, as the Paramecium; while others, like 
the vorticella, are attached, yet possess distinct and remark- 
able movement, within a certain limit. All collect food and 
assimilate it and grow as any other animal. Each one 
breathes, of course in a primitive manner; but, neverthe- 
less, oxygen is taken in, and carbonic acid given off as 
regularly as among the higher animals. 

If we jar the slide on which the vorticella is placed, the 
tiny animal will suddenly roll into a ball and dart back to its 
place of support. We have already seen how the amoeba re- 
acts toward food and avoids a grain of sand. Paramecia 
are sensitive to an electrical current. Hence we see that 

hertuck's zool. — 3 



34 AMCEBA, VORTICELLA, PARAMECIUM 

all of these simple animals have sensation, because they 
respond to irritation. 

Another thing is important to note in our study of the 
foregoing animals. Beginning with the amoeba, we went 
steadily upward to higher and more complex forms. The 
amoeba had no wall, all the others had. The amoeba had 
no mouth, all the others had. The amoeba moved slowly 
and in a very primitive way, the Paramecium faster, while 
the vorticella had the most complex movement of all. 
Moreover, it will be recalled that the amoeba moved in any 
direction, and that almost any part of the body seemed 
capable of bringing about this movement. The amoeba 
has no sharply defined anterior and posterior ends, and no 
right and left sides. The Paramecium has a posterior and 
anterior end and moves principally in one direction with a 
definite part of its structure foremost. 

Economic importance of the Protozoa. — Although the 
protozoans are microscopic in size, some of them exercise 
a very profound influence upon the life relations of man. 
Occasionally certain species become so numerous in drink- 
ing water that the water is rendered unfit for use. A species 
of amoeba is known to sometimes occur in the intestinal tract 
of man and has been thought, by some, to be the cause of 
dysentery. 

Texas fever, so universally present among the cattle of 
the Southern states, is caused by one of these microscopic 
animals. This organism is injected into the blood of an 
animal and carried from one animal to another by the 
common cattle tick. Whenever cattle south of what is 
known as the tick line come in contact with cattle north of 
that line, the latter are inoculated by the tick and usually 
die. 



AMCEBA, VORTICELLA, PARAMECIUM 35 

It has been demonstrated that a certain protozoan, in- 
jected into the blood of man by mosquitoes, causes the 
disease, malaria. The parasite lives within the red blood 
corpuscles, destroying great numbers of them and finally in- 
ducing chills and fever, and in many cases causing death. 
The life history of the malarial parasite is interesting and 
complex. Part of its life is spent in the body of certain 
species of mosquitoes and part in the human blood. That 
jis, the full development of the malarial • parasite cannot 
take place in the human blood, but a secondary host, 
the mosquito, is necessary in order that the complete life 
history of the parasite may be undergone. 

CLASSIFICATION OF THE EXAMPLES 

Branch I — Protozoa. 
Class — Sarcodina. 

Order — Amoebida. 
Types of Order : 

Amoeba proteus — Amoeba. 
Globigerina bulloides — Globigerina. 
Class — Infusoria. 

Order — Holotrichida. 
Type of Order : 

Paramecium aurelia — Slipper animalcule. 
Order — Heterotrichida. 
Type of Order : 

Stentor polymorphus — Stentor. 
Order — Peritrichida. 
Type of Order : 

Vorticella nebulijera — Bell animalcule. 
Class — Sporozoa. 

Order — Hsemosporidiida. 
Type of Order : 

Plasmodium malarias — Malarial parasite. 



VI. SPONGES 
Branch II. — Porifera (porce, pores; Jerens, bearing) 

All sponges live in water, either fresh or salt. The fresh- 
water sponges may be found in rivers, lakes, ponds, etc> 
probably in every country in the world. The marine 
sponges are very widely distributed in the sea and occur at 
nearly all depths, from the shallow to the very deep parts 
of the ocean. In some parts of the sea they are exceedingly 
abundant. They are of multitudinous forms, individuals 
of the same species varying greatly in shape. Some are 
flat, some are globular, some are treelike in shape, others 
are vaselike in form, while some are cylindrical. This va- 
riation in shape is due largely to the fact that they are easily 
modified by surrounding conditions. A change in current 
or a change in the character or shape of the sea bottom will 
almost surely bring about a change in the shape of these 
animals. When the young marine sponges are first hatched 
from the egg, they are, for a time, free, and they can move 
about through the water. They soon become attached 
and for the rest of their lives remain stationary. Hence 
sponges may be said to be fixed animals. 

Structure of a simple sponge. — The simplest sponge 
that we know anything about is vase-shaped, with the 
lower end contracted into a sort of stalk by which the ani- 
mal is attached. Generally speaking, the body is a hollow 
cylinder, closed at the lower end but open at the opposite, 



SPONGES 37 

or free end. Scattered over the surface of the sponge are 
small rounded apertures, which are the openings of short 
pores, that pass directly through the body walls into the 
central or body cavity. These pores are called the in- 
halent pores because the water flows through them 
into the body cavity. From thence the water passes out 
through the large opening, or osculum — exhalent pore — 
at the free end of the sponge. Thus there is a continuous 
circulation of water through the body of this simple animal. 
The body wall consists of three distinct layers, an outer 
layer, consisting of flat cells closely joined to each other 
and covering the outside of the body; an inner layer, 
of much thicker cells, lining the body cavity ; and between 
these two, a layer of whitish, soft, gelatinous substance with 
cells of various shapes imbedded in it. Each of the cells 
composing the inner layer of tissue has a long, lashlike 
appendage, called a flagellum, that projects from the end 
of the cell into the large body cavity. These flagella are 
constantly waving, or lashing, and in this way they main- 
tain currents of water that bring bits of organic food to the 
animal. All three layers of the body are soft, especially the 
middle one, and if the sponge had nothing rigid to support 
it, the body would collapse. Imbedded in the middle, 
gelatinous layer, are slender, glassy, needlelike bodies com- 
posed of lime carbonate, and known as spicules. These 
constitute the skeleton, as it were, and support the body. 

A More Complex Example of the Branch — the 

Simple Sponge, Grantia 

Distribution. — Grantia is a simple sponge found along 

the Atlantic and Pacific coasts. It occurs in small groups, 

attached to submerged rocks or other objects below low- 



38 



SPONGES 



water mark. It is easily obtainable for study, while the 
simpler sponge is not. 

External features. — The body is about one half an inch 
in length, cylindrical in shape, and fixed by one end, while 
the opposite end is furnished with a small opening, the 
excurrent opening, or the osculum (Fig. 13) . The osculum is 

surrounded by a col- 
lar of long, white, cal- 
careous, needlelike 
spines called spicules. 
Structure of the 
body. — The body is 
a hollow cylinder 
with rather thick 
walls. The large cen- 
tral cavity, or cloaca, 
extends throughout 
the length of the 
body and opens out- 
ward through the 
osculum. The body 
walls are perforated 
with two sets of par- 
allel canals that run at right angles to the cloaca. One 
set, the inhalent canals, runs from the outside of the 
body almost to the cloaca and ends blindly. The other 
set, the radial canals, begins at the cloaca and runs par- 
allel with the inhalent canals, but ends blindly just before 
reaching the outside of the body. These canals run side by 
side and communicate with each other by minute pores 
through their adjoining walls. The water enters the inha- 
lent canals through the incurrent pores, the mouths by 




Fig. 13. — Sponge (Grantia) : A, an individual 
split lengthwise showing body cavity (be), in- 
halent pore (it), osculum (o), circle of spic- 
ules ( c) ; B, two individuals attached to a stick. 



SPONGES 



39 



which these canals open outward, passes through fine open- 
ings in the walls of the former directly into the radial canals, 
from which it escapes into the cloaca and thence outward 
through the osculum. 

Body walls. — The body walls of Grantia are much thicker 
than those of the simple sponge,, and the pores are 
longer. There are three layers of tissue similar to those of 
the simple sponge, already described. 

The inner layer, lining the radial canals, has its cells 
peculiarly modified in structure, and they are known as 
collar cells. Moreover, each collar cell possesses a long 
vibratile flagellum. All of these flagella are constantly 
waving with lashlike vibrations and thus maintain cur- 
rents of water through the canals. 

Skeleton. — Like the simple sponge, Grantia has its body 
supported by a mass of interlaced spicules, composed of 
lime carbonate (Fig. 
14). Two kinds of 
spicules are always 
to be found, — tri- 
radiate and needle- 
shaped. The tri- 
radiate spicules are 
interlaced and inter- 
woven in the middle 
layer of the body 
walls so that they FlG ' 14 ~ Sponge spicules - 

form a skeleton or supporting framework. The needle- 
shaped spicules are found projecting through the outer 
layer of cells all over the body. 

Method of feeding. — This sponge feeds upon micro- 
scopic bits of plant and animal organisms, floating in the 




40 SPONGES 

sea. The currents of water entering the incurrent pores are 
laden with these minute organisms, which are taken up by 
the collar cells of the radial canals and digested. There 
are no special organs of digestion, but each of these cells 
gathers and digests its own food. 

Method of breathing and excretion. — The same currents 
of water that bring food also carry fresh oxygen, which is 
given up to the cells as the water passes over them. At the 
same time, the cells give off carbonic acid gas, which is car- 
ried outward by the water, and thus the sponge breathes. 

The particles of undigested food are carried out through 
the osculum by the currents of water. Whatever waste sub- 
stances the cells excrete are got rid of in the same way. 

Reproduction and life history. — Grantia reproduces by 
budding. That is, a bud forms on the external surface of 
the body, which gradually increases in size and grows into a 
new sponge individual. In the case of Grantia these bud 
sponges break away from the parent, become attached, and 
pass a solitary existence. In some sponges they remain 
attached to the parents and thus there comes to be formed 
a large colony of individuals. 

Grantia also reproduces in a sexual manner, although 
" specialized reproductive organs are not present. The 
sexual elements will be found in the form of large spherical 
bodies in the wall of the sponge. Fertilization takes place 
here, and development begins, and the young embryos 
escape into the sea water through the canals. For a while 
the embryo is a free-swimming animal, but it finally fastens 
itself to a rock and develops into the adult sponge." 

Structure of other sponges. — All sponges may be said 
to have the three layers of tissue found in the simple sponges; 
but, in other respects, the structure of the body in the 



SPONGES 41 

higher sponges is much more complicated. In the higher 
sponges there is no general body cavity, but the whole 
sponge mass is full of large tubes, each with its osculum. 
Moreover, there are innumerable inhalent pores leading into 
special pockets, or chambers in which the flagellated cells 
are situated. Recall that the flagellated cells in the very 
simple sponge are situated in the general body cavity. 
The chambers containing the cells with flagella communi- 
cate, by small canals, with the large tubes. Thus there is 
provision for the same circulation of water as in the simple 
sponges. Sponges are of various colors. They may be red, 
orange, blue, purple, green, and gray. 

Fresh-water sponges. — Most of the sponges are found 
in the sea, but a few live in fresh water. The fresh- water 
species are very widely distributed in lakes, ponds, rivers, 
etc., hence they may be found in many localities. Repro- 
duction is brought about by a budding process. A spherical 
mass of cells, surrounded by a hard siliceous case and known 
as a gemmule, is formed within the body of the parent 
sponge. In the autumn this bud, or gemmule, is set free in 
the water by the decaying of that part of the body in which 
the gemmule lies. The gemmule, after being set free, settles 
to the bottom of the water, where it passes the winter. With 
the change in temperature in the spring, the cells within 
the case escape through the natural hilum, or orifice of the 
gemmule, begin growing, and soon develop into a mature 
sponge. The fresh- water sponges belong to the family 
Spongillidse. / 

Skeletons of sponges. — Some sponges have no skeleton. 
In those sponges in which a skeleton exists, it is formed by 
the cells of the middle layer and may consist of different 
substances. In some, the skeleton is formed from spicules 



42 



SPONGES 



composed of silica; in others, the skeleton is formed from 
spicules composed of lime carbonate; while in others, it 
is formed from fine, flexible fibers of a substance called 
spongin, which is allied to silk in chemical composition. 
Those sponges which have a skeleton composed of silica are 
harsh and unfit for domestic purposes. Those with skele- 
tons of spongin are soft and are used for various domestic 
purposes. See Figure 14 for spicules of various shapes. 

Siliceous sponges. — The most beautiful of marine 
sponges have skeletons composed of silica. The spicules 

are like spun glass, 
and in the sponge, 
known as the Venus's 
basket, they are ar- 
ranged so uniformly 
that the skeleton re- 
sembles a piece of 
fine lacework (Fig. 
15, E). This sponge 
is found growing 
near the Philippines 
in about ten fathoms 
of water. 

Another one, some- 
times called the glass- 
rope sponge (Fig. 15, 
H), has a long stem 
composed of the long, 
white, glassy spicules 
twisted together. 
The sponge body grows on the upper end of this stem, 
while the lower end of the stem is anchored in the mud. 




Fig. 15. 



E, Venus's basket sponge ; H, glass- 
rope sponge. 



SPONGES 43 

Sponges of commerce. — The sponges that we see in the 
drug stores are nothing but the interlaced masses of soft, 
flexible, spongin fibers that compose the skeletons. Our 
best sponges come from the Mediterranean, the next best 
from the Red Sea, and a poorer quality from the Bahamas, 
West Indies, Key West, and west coast of Florida. In 
gathering them for market, they are pulled from the rocks 
with pronged hooks attached to poles whose length is at 
least as great as the water is deep. In deep waters, divers 
go down and gather them off the rocks. After being col- 
lected they are either exposed to the air until the soft parts 
decay, or they are thrown into kraals, or cribs, near low- 
water mark, and left where the tides wash through them, 
until the fleshy parts pass away. They are then bleached, 
dried, and sent to market. 

Relation of sponges to other animals and to their en- 
vironment. — Sponges were originally thought to be 
colonial Protozoa, but it has now been determined that they 
produce eggs and that these eggs, during development, first 
divide into two cells, these into four, these into eight, these 
into sixteen, and from these the mature sponge finally de- 
velops. Such a mode of development certainly excludes 
them from the one-celled animals. At the same time, the* 
sponges are the simplest of the many-celled animals. The 
one cell of the Protozoa does everything, but in the sponges 
some cells gather food, other cells perform reproduction, 
while others digest food. These different cells, each de- 
pendent upon the other, are joined together to form an 
organized but simple body in comparison with other met- 
azoans. 

It is evident that the sponges could not live on land be- 
cause they are fixed and food must be brought to them, and 



44 SPONGES 

water is the most suitable agent for carrying food. The 
sponge is furnished with cells bearing flagella which, by 
their movements, maintain currents of water laden with 
food. 

Economic importance of the sponges. — A few sponges 
have formed the habit of boring into limestone rock and 
into the shells of certain mollusks, but the destructiveness 
of these few is probably not great. On the other hand, 
the commercial trade in sponges is large. The sponge 
fisheries in the Mediterranean Sea give employment to 
thousands of people, and the receipts from sponges sent to 
foreign markets amount to thousands of dollars annually. 
The value of the sponges handled in Trieste, alone, in one 
year, amounts to nearly two hundred thousand dollars, 
and the demand for sponges is continually increasing. 
Moreover, there are the sponges from the Bahamas, Red 
Sea, and West Indies that must be taken into account in 
any reliable estimate of the economic value of sponges. 

CLASSIFICATION OF THE EXAMPLES 

Branch II — Porifera. 
Class — Porifera. 

Ascetta primordialis — Simple sponge. 
Grantia ciliata — Simple sponge. 
Euplectella aspergillum — Venus's basket. 
Hyalonema longissimwn — Glass-rope sponge. 



VII. HYDR.E, JELLYFISHES, SEA ANEMONES, 
CORAL POLYPS 

Branch III. — Ccelenterata (koilos, hollow ; enteron, 
intestine) 

The Ccelenterata, which include the corals, jellyfishes, 
sea anemones, etc., occur, without exception, in the water, 
and the majority of them are found in the sea. In general 
they are much more complex in structure and development 
than the sponges, but resemble the sponges in several 
respects, namely, in the tendency to reproduce by budding 
and form colonies ; in their fixed mode of life ; and in the 
possession of one body cavity. Perhaps the corals are the 
most familiar examples of this group, but there are many 
other little-known members, the characters of which will 
be better understood after the study of a few leading 
types. 

An Example of the Branch— the Fresh-water 
Hydra 

Where the hydra lives. — The fresh- water hydra lives in' 
ponds, pools, ditches, and streams where there is an abun- 
dance of water plants, such as duckweed, algae (pond scum), 
etc. There are two species of hydrse that are common, 
the green hydra and the brown hydra. 

External features. — The hydra has a long, cylindrical 
body attached to some part of a submerged water plant 
or other object by the posterior end, while the anterior end 
sways free in the water. The mouth is situated at the 

45 



46 HYDR^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 



anterior end and is surrounded by five to eight slender ap- 
pendages, the tentacles. These are often as long as the 
body (Fig. 16). 

Movements and locomotion of the hydra. — Although the 
hydra, for t the major part of its time, remains fixed by its 

posterior end to some 
submerged object, 
yet, even in this 
position it is capa- 
ble of considerable 
movement. For ex- 
ample, the body can 
be contracted until 
it appears like a tiny 
ball or extended until 
it reaches half an inch 
in length. Likewise, 
the tentacles may be 
contracted until they 
appear as small knobs 
about the mouth or 
extended until they 
become very slender 
and as long as the 
body. Moreover, the 
body and tentacles 
sway about through 
the water in search 
of food. 




Fresh-water hydra fully expanded. 



It must be remarked that the hydra has no muscle fibers 
like those of the higher animals with which movement is 
brought about. But many of the ectoderm cells have their 



HYDR^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 47 

inner ends extended into narrow prolongations that run 
at right angles to the body of the cells. These narrow pro- 
cesses are called the muscle processes because they possess 
highly developed contractile power, and they serve to con- 
tract and expand the body. 

The body of the hydra is attached by means of a sticky 
substance secreted by the posterior end, or foot. At times 
the hydra breaks this connection and moves in a peculiar 
manner to another location. It stretches out as far as 
possible, bends over, and grasps hold with its tentacles. 
Then it pulls the foot of the body close to the place where it 
has taken hold, thus forming itself into a loop. By repeat- 
ing this action, it moves from place to place after the man- 
ner of a " looping," or " measuring" worm. At other times 
it takes hold with the tentacles and swinging the posterior 
end of the body slowly through the water turns a complete 
somersault. Then, occasionally, it crawls slowly along by 
means of its tentacles alone. 

Structure of the body. — The body of the hydra is a 
long, cylindrical sack, closed at one end and open at the 
other. The walls of the body are composed of three layers 
of tissue: an outer layer of cells, the ectoderm; an inner 
layer of cells, the endoderm; and between these two layersj 
a third layer, of gelatinous, non-cellular tissue called the 
mesoglcea. The body cavity, or digestive cavity, since in 
this animal they are one and the same, extends throughout 
the whole length of the body and opens outward through 
the mouth between the bases of the tentacles. The tenta- 
cles are also hollow and open into the body cavity (Fig. 17). 

Method of obtaining food. — There are in the ectoderm of 
the body, and especially of the tentacles, certain large cells, 
known as the stinging thread cells. Each stinging cell con- 



48 HYDRJE, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 



tains an ovoid capsule filled with a peculiar, irritating 
fluid. Within the capsule and surrounded by the fluid 
is a long, slender, hollow thread coiled into a spiral. If, by 
chance, a foreign body — for instance, a tiny crustacean — 
comes in contact with a tentacle, the latter is stimulated to 

action and quickly 
winds about the for- 
eign body. Then from 
each stinging cell the 
coiled thread, which is 
hollow, quickly rolls 
out and pierces the 
skin of the captive. 
The poisonous fluid 
is then discharged di- 
rectly into the wound 
through the hollow 
in the thread. 

Means of protec- 
tion. — The hydra also 
protects itself from 
its enemies by means 
of the stinging thread 
cells. When an ene- 
my approaches within 
reach, the stinging 
threads are shot out from many different cells, and the 
antagonist, if not too large, is overcome by the poisonous 
fluid. Even if not overcome, the enemy is often frightened 
into retreat. 

How the hydra breathes. — This primitive animal has 
no special organs of respiration. It takes oxygen into its 




£ig. 17. — Diagrammatic drawing of a hydra : 
A, stinging thread cell; B, bud; C, body- 
cavity. 



HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 49 

body through all parts of the surface and gives off car- 
bonic acid gas from all of its cells. In other words, each 
cell of the body performs the act of breathing for itself, 
independently of every other cell. 

How the hydra digests its food. — The food, as we have 
seen, enters the mouth and passes directly into the large 
digestive cavity, which is uniform throughout its whole 
length and not differentiated into stomach, intestine, etc. 
But some of the endoderm cells lining this cavity secrete 
a digestive fluid which breaks up and dissolves the food 
to some extent. Probably particles of this food are then 
taken up by other of the endoderm cells and digested 
within them by their own protoplasmic mass. The ecto- 
derm cells obtain their nourishment from the nutritive 
matter in the endoderm cells. 

The hydra's manner of excretion. — There is only one 
opening to the body of the hydra and all undigested por- 
tions of food are passed outward through the mouth, the 
same route through which they entered the body. As we 
have seen, carbonic acid gas is given off through all parts 
of the surface. There are no special organs of excretion. 

Reproduction of the hydra. — These little animals repro- 
duce by budding and by eggs. An individual is often found 
with a smaller hydra growing out from the side of its body. 
The smaller one arises by a process of budding. The body 
wall of the parent bulges out at some point, forming a bud- 
like protuberance which enlarges and develops at its free 
end a mouth and tentacles, thus becoming a well-developed 
hydra (Fig. 17). The body cavity of the young hydra is 
continuous with that of the parent (Fig. 17). After a time 
these bud hydrae become detached and they then pass a 
separate existence. 

herrick's zool. — 4 



50 HYDR^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 

True eggs are also produced by the hydra. The ovary 
containing the ova is situated in the body walls near the 
posterior end of the body. The sperm cells are produced in 
the walls just below the tentacles. When mature, the 
ovum is fertilized by the sperm, settles to the bottom, and 
after lying dormant awhile develops into an adult. 

Regeneration of lost parts. — Many animals are similar to 
plants in their ability to reproduce lost organs and parts. 
If a hydra is cut in two near the middle, each part will re- 
produce the lost part, thus producing two hydrse where 
formerly there was one. If a hydra is cut into several pieces, 
each piece, under favorable conditions, will produce a new 
hydra. Where conditions are favorable to life, a hydra 
can hardly be killed by mutilation. Hydrae may be cut 
into pieces and the pieces may be grafted together in all 
sorts of ways and yet thrive and grow vigorously, as 
related by Professor Morgan in his interesting book on 
f - Regeneration." 

The Campanularian Hydroid 
Class I. — Hydrozoa (water animals) 

The branch Ccelenterata is divided into several classes, 
representatives of which will be briefly discussed and com- 
pared with the hydra. 

The hydrozoans are Coelenterata living in water, either 
fresh or salt. Some of them are simple in structure, like 
the hydra, and some of them are very complex, both in 
structure and development. 

Campanularian hydroid. — This is an exceedingly delicate 
and beautiful organism found growing in the sea attached 
to seaweeds, rocks, sunken timbers, etc. It is known as a 



HYDR^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 51 



colonial animal because it is made up of two kinds of " in- 
dividuals/' or, as they are called, zooids, each kind of zooid 
having a special func- 
tion to perform. The 
zooids are borne on 
a common, slender 
stem, or axis, and one 
kind is known as the 
nutritive zooids while 
the other kind is 
known as the repro- 
ductive zooids. 

The axis may be 
said to consist of two 
portions, a horizontal 
portion which runs 
over p the rocks and 
weeds in a horizontal 
direction (Fig. 18, a), 
and a vertical portion 
which consists of ver- 
tical stems arising 
from the horizontal 
part of the axis. 
Moreover, the verti- 
cal stems give off 
lateral branches in an 
alternate manner and 
the nutritive zooids 
are borne on the outer ends of these lateral branches. All 
of the different portions of the axis are about the size of 
cotton threads, hence this animal is visible to the unaided 




Fig. 18. — Campanularian hydroid : a 4 horizon- 
tal branch ; pr, perisarc ; rp, reproductive 
zooids ; nt, nutritive zooid ; c, coenosarc. 



52 HYDTUE, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 

eye. Because of the alternate lateral branching of the 
vertical stems, the animal shows a striking resemblance to 
a plant. 

Usually, near the base of the vertical stem bearing the 
zooids will be found one or more club-shaped cavities, 
formed at the ends of short lateral branches. These cap- 
sules are closed at the free ends and contain within them the 
reproductive zooids (Fig. 18, rp). While within the trans- 
parent capsule the reproductive zooids are mere buds and 
are called medusa buds. After a time the capsules break 
open and the medusa buds pass out, one by one, and are 
then known as medusce, and sometimes jellyfish. They 
are umbrella-shaped and are found floating with the convex 
side uppermost. 

After a time these medusae produce eggs that finally 
develop into the plantlike, colonial organism with which 
we started. 

Jellyfishes 

Glass II. — Scyphozoa (cuplike animals) 

Nearly all of the large jellyfishes belong to this class 
and, in general, it may be said that the members of 
this class are larger than those of the Hydrozoa. Moreover, 

the majority of 
the Scyphozoa swim 
freely on the surface 
of the ocean. A 
few are found to 
inhabit the ocean 

Fig. 19. — Jellyfish (A urelia). a t great depths. 

The common jellyfish, Aurelia. — This is a true jellyfish 
and has a convex, tough, jellylike body and is often found 




HYDROS, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 53 



floating on the surface of the sea (Fig. 19). In the center 
of the under surface of the body is the mouth. Above 
the mouth is the stomach, 
and higher up, from the end 
of the digestive cavity, canals 
radiate like the ribs of an 
umbrella. These canals extend 
downward along the inside of 
the dome and finally com- 
municate with a circular canal 
around the edge of the disk. 
This system of tubes is suggestive of the water vascular 
system of the echinoderms. 

Aurelia has an interesting and complex life history. The 
adult produces eggs, each of which hatches into a ciliated 




Fig. 20. 



-Embryo of jellyfish 
(Aurelia). 




Fig. 21. — Hydralike stage of Aurelia. After Agassiz. 



embryo (Fig. 20). The embryo soon attaches itself to a 
rock and transforms to a hydralike animal about one half 



54 HYDR.E, JELLYFISHES, SEA ANEMONES, CORAL POLYFS 

an inch high (Fig. 21). After eighteen months this form 
begins to increase greatly in length and becomes marked 
off into many transverse divisions by circular, transverse 
constrictions so that it resembles a pile of saucers with 




Fig. 22. — Hydralike stage 
of Aurelia ; saucer forms. 
After Agassiz. 



Fig. 23. — Saucer stage of Aurelia. 



scalloped edges (Fig. 22). Finally, each division, or saucer, 
breaks away, swims off, and is known as an ephyra (Fig. 
23). The ephyra, with a few changes, soon develops into 
the adult, umbrella-shaped jellyfish. 

Sea Anemones, Coral Polyps, etc. 

Class III. — Actinozoa {raylike animals) 

The Actinozoa occur in the sea, in both deep and shallow 
water, and are often of brilliant hues. They are of the same 
general structure as the hydra, but differ in that the mouth 
opens into a short, distinct gullet, which, in turn, opens be- 
low into the stomach, or body cavity. They also differ in 



HYDR^E, JELLYEISHES, SEA ANEMONES, CORAL POLYPS 55 



having vertical partitions that divide the lower part of the 
body into distinct compartments. In these two respects 
the Actinozoa show a decided advance over the Hydrozoa 
and the Scyphozoa. 

Sea anemone. — There are many species of sea anemones, 
but a common one, known as Metridium (Fig. 24), will 
serve as an example, 
since they are all 
much alike. This one 
is found along the 
seacoast from Maine 
to New Jersey, at- 
tached to piles of 
bridges, rocks, or 
sunken timbers. Me- 
tridium has a soft, 
leathery, cylindrical 
body, varying from 
three to eight inches 
in diameter, when 
fully expanded. At 
the base, this cylinder 
is slightly expanded to 
form a large sucker, 
by means of which the animal attaches itself. The free 
end of the body is covered by a membrane and has a 
thick crown of tentacles, arranged around the edge, leaving 
an open space in the middle, in the center of which is an 
aperture, the mouth. This opens directly into the gullet, 
which is an oval sack suspended from the membrane cover- 
ing the end of the body. The gullet opens below into the 
stomach, or body cavity. The gullet does not hang freely 




Fig. 24. — Sea anemone. 



56 HYDY^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 

suspended, but is supported by numerous radial partitions 
that extend from it to the body walls. Between these are 
other partitions that do not reach the gullet, one edge being 
free (Fig. 25). The reproductive organs are attached to the 
faces of these vertical partitions. The tentacles are hollow 
and open directly into the body cavity. They are expanded 

by a contraction of the* 
body wall, which forces 
the water contained in the 
body cavity up into the 
hollows of the tentacles, 
thus causing them to ex- 
tend and enlarge. The 
food is caught by the 
tentacles and passed into 
the mouth. The whole 
body, when the animal 
becomes alarmed, con- 

Fig. 25. — Diagram of a cross section of a tracts and shrinks into B> 

sea anemone. shapeless mass, by aid 

of its muscle fibers after the water is expelled. When all 
is quiet again, it slowly draws in water, and gradually 
expands to its former size. 

Other sea anemones. — There are many species of sea 
anemones and they are of various sizes and colors. They 
are abundant along the seacoast, and resemble flowers so 
much that they are popularly known as "sea flowers." 
Most sea anemones can detach themselves and move from 
place to place. The tentacles are constantly but slowly 
moving, and often, when stimulated by contact with foreign 
substances, they attempt to carry the particles to the mouth 
of the animal. 




HYDK^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 57 

Coral polyps. — Most of the sea anemones are simple, 
i.e. each animal is separate, living by itself, although it 
may reproduce by budding. On the other hand the coral 
polyps, although they are very similar to the sea. anemones 
in structure, are usually compound, and live in colonies. 
These are the animals that mainly build up the great coral 
reefs, found so abundantly in the Pacific Ocean. The 
structure of each little animal, or polyp, as it is called, is so 
similar to that of the sea anemone that it needs no further 




Fig. 26. — Corals : A, tree coral ; B, tree coral ; C, head coral. 

description here. A coral polyp differs from a sea anemone 
greatly in one particular, however; viz. in the power to 
secrete lime carbonate. This mineral substance is secreted 
by the ectoderm of the lower part of the polyp. In a large 
colony of polyps in which new individuals are constantly 
appearing, and in which each individual is adding its share 
of lime carbonate to the secretions of the others, there is 
finally built up in the process of time a great mass of lime 
carbonate. The shape of this mass will depend upon the 
species of polyp building it. 



58 HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 



It must be borne in mind that coral reefs are not always 
built by coral polyps alone. Other animals and often- 
times certain plants aid greatly in building up reefs. Never- 
theless, the principal reef builders belong to the group of 
animals known as coral polyps. Some of the species of 
corals grow and branch like a tree. (Fig. 26), finally attain- 
ing a great size and 
producing an im- 
mense coral forest, 
as it were, which, in 
time, may reach the 
surface of the sea. 
In such an event the 
ends of the living 
branches of coral 
may extend out of 
the water at low tide. 
The waves then break 
off pieces of coral, 
which, together with 
other debris floating 
on the sea, fill up the 
spaces between the 
ends of the branches 
until the top of the 
More material 




Fig. 27. 



Diagram of coral reefs. 

reef becomes a solid, smooth surface. 



lodges on top, seeds fall there, and finally the reef becomes 
clothed with verdure. 

There are three kinds of coral reefs; viz. fringing, 
barrier, and circular reefs, or atolls. A fringing reef 
(Fig. 27, A) lies close to the shore of an island or conti- 
nent. A barrier reef (Fig. 27, B) is separated from the 



HYDR^E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 59 



&&k&kz 



mainland by an intervening lagoon of water of varying 
depth and width. An atoll is, generally speaking, an oval 
reef inclosing a lagoon of water but no land (Fig. 27, C). 

Coral polyps, with few exceptions, cannot live more than 
fifteen or twenty fathoms below the surface of the water, 
or in water that goes below 68° F. in temperature, or in 
fresh or in muddy water. Therefore, in order that the 
polyps may begin a reef, they must have rock for a founda- 
tion that is not over one hundred 
and twenty or thirty feet below 
the surface of the clear, briny sea. 

Not all corals, by any means, 
build reefs. Some polyps bud in 
such a manner as to form hemi- 
spherical masses of coral, varying 
from a few inches to several feet 
in diameter. Such an aggregation 
of polyps is called a head coral 
(Fig. 26). Other globular masses 
have their outer surfaces covered 
with serpentine furrows which 
cause them to resemble brains, 
hence they are called brain corals. 

The organ-pipe coral (Fig. 28) builds up a series of 
deep red tubes arranged side by side and held together 
by horizontal floors. 

Finally, there is the red coral of commerce, which 
was formerly so largely used for ornament. Of course 
the red part worn is but the hard lime secretions of the 
little polyps. When living, these red branches are wrapped 
in a layer of flesh much as the wood of a tree is wrapped in 
bark. The polyps, which are creamy white and have eight 




Fig. 28. — Organ-pipe Coral 
(Tubiporamusica). Indian 
Ocean. 



60 HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 

tentacles, live in small holes in this layer of flesh, at right 
angles to the red stem within. When undisturbed, they 
project beyond the opening with tentacles spread out to 
catch food; but when irritated, they withdraw into the hole 
for protection. 

Sea Walnuts 
Glass IV. — Ctenophora (comb bearers) 

These are peculiar jellyfishes, mostly small, which spend 
a free-swimming life and, so far as is known, never form 
colonies. Neither is there at any stage of their existence 
a polyp form as in other Coelenterata we have studied. 
These organisms are extremely delicate and are usually 
perfectly transparent. They swim by means of cilia and 
many of them are highly phosphorescent. 

Alternation of generations among the Coelenterata. — Like 
many of the lower plants — fungi, mosses, and ferns — 
many of the lower animals show what is known as an 
alternation of generations. This phenomenon is shown by 
the campanularian hydroid, the aurelia, and other ccelen- 
terates of which we have not spoken. It will be recalled 
that a generation of each of two dissimilar individuals 
— the plantlike form and the medusa — was necessary 
to complete the full life history of the campanularian 
hydroid. Moreover, these generations followed each other 
alternately; the medusa giving rise to the plantlike struc- 
ture, and the plantlike structure giving rise to the 
medusa, and so on indefinitely. Again, the campanularian 
hydroid may be said to exist under two different forms. 
This is called dimorphism (di, two; morphe, form). Some 
animals that exist under more than two forms are said to 
be polymorphic. 



HYDRiE, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 61 

Relation of this branch to the sponges. — The members 
cf this branch resemble the sponges in their fixed mode of 
living, in their manner of forming colonies by budding, in the 
possession of one body cavity, and in certain other ways too 
intricate to mention here. Hence, it seems that this branch 
stands nearer the sponges than any other branch of the 
Metazoa, but is higher in the scale than the sponges. For 
instance, we find the beginnings of a nervous system. In. 
some of the jellyfish the nervous system consists of two 
rings of nerve matter around the edge of the umbrella. 
This is the first example of a concentrated, well-defined 
nervous system. The nervous system in the sea anemones 
consists of nerve cells and fibers irregularly disposed 
throughout the body. The methods of reproduction are 
more specialized than in the sponges, as are also the mode 
of living and the life history. 

Adaptations to mode of living and environment. — An 
animal, to live, must have food. This food must either be 
brought to the animal, or the animal must go to it. Many 
of the animals in the foregoing branch are fixed and cannot 
go to their food. Such members have long, slender ten- 
tacles with which they can catch the food as it passes by 
and convey it to the mouth, — notably the fresh- water 
hydra. The hydractinia, a complex coelenterate, is even 
better adapted than this. It attaches itself to the shell of 
the hermit crab, and is thus carried to new fields of food. 
At the same time it falls heir to minute morsels of the 
crab's food. It pays for all this, however, by affording 
protection to the crab, of which we shall speak later. 

It will be remembered that nearly all of the Coelenterata 
are soft-bodied animals. In the ocean they are always 
surrounded by hordes of enemies, who would quickly 



62 HYDPwE, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 

devour them, were it not for the stinging cells with which 
they are all so plentifully provided. The Portuguese man- 
of-war is even dangerous for a man to handle. At the 
same time the thread cells furnish splendid weapons for 
paralyzing the prey used as food. 

It is said that small fishes, as the butterfish, swim be- 
neath the bell of one of our large jelly fishes for the purpose 
of being protected. This may be taken as good proof that 
the protection afforded by the thread cells is effective. 

Economic importance of the coelenterates. — Perhaps 
the ccelenterate that represents the most direct economic 
importance is the one that produces the red coral used for 
ornament. The main coral fisheries are on the coasts of 
Algiers, Tunis, and Morocco. Naples is the center of the 
coral trade. The prices vary according to color. Large 
pieces of the finest rose pink are valued at from four 
hundred to five hundred dollars an ounce, but small pieces 
of the paler colors, used for children's necklaces, are 
worth one dollar to one dollar and a half an ounce. 

Indirectly, the different species of coral polyps are of 
economic importance because of the extensive areas of 
land built up by them. Many islands in the Pacific are 
examples of this land building through the agency of 
coral polyps. The most noted example, in our own 
country, of the part played by coral polyps in building 
up land is found in the present State of Florida. Much 
of the southern part of this State has been formed through 
the agency of these small animals. This has been accom- 
plished through successive lines of coral reefs built par- 
allel with the shore of the mainland, and through the 
filling up of the open channels between with silt, drift- 
wood, and other decaying material. 



HYDR.E, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 63 



CLASSIFICATION OF THE EXAMPLES 

Branch III — Coelenterata. 
Class — Hydrozoa. 

Order — Hydromedusae (Leptolinse). 
Types of the Order. 

Hydra viridis — Hydra. 
Hydractinia echinata — Hydractinia. 
Obelia dichotoma — Campanularian hydroid. 
Order — Siphonophora. 

Physalia arethusa — Portuguese man-of-war. 
Class — Scyphozoa. 

Order — Discomedusse. 
Type of Order. 

Aurelia flaviduia — Jellyfish. 
Class — Actinozoa. 

Order — Actinaria. 
Type of Order. 

Metridium dianthus — Sea anemone. 
Order — Madreporaria. 
Type of Order. 

Madrepora formosa — Coral pol} T ps. 
Class — Ctenophora. 
Order — Cydippida. 
Type of Order. 

Pleurobrachia rhododactyla. 



VIII. FLATWORMS, ROUNDWORMS, AND 
ROTIFERS 

Branches IV, V, VI, and VII. — Platyhelminthes (Flat- 
worms), Nemathelminthes (Roundworms), Trochelmin- 
thes (Rotifers), and Molluscoidea (Lamp Shells) 

In this chapter we shall discuss examples of four branches 
the members of which, heretofore, have all been included in 
one branch, Vermes (worms). The individuals, commonly 
placed in the branch Vermes, differ so much among them- 
selves that the later authorities put them in different 
branches. The members of the above branches are more 
or less wormlike in character and appearance. The body 
of the earthworm, as we know, is divided into rings, or 
segments; but no true segments are found in the simpler 
worms. The animals treated in this chapter are perhaps the 
most widely distributed of all the many-celled animals. 
Some are found from the shallowest to the deepest water 
in rivers, lakes, and seas; some live on the land; while 
some live as parasites in many different species of the 
multicellular animals. 

Flatworms 

The flatworms include a great variety of forms that 
differ widely from each other in habits and appearance. 
The majority have flattened, more or less leaflike bodies; 
a few have approximately cylindrical bodies. The fresh- 
water flatworms, found on the bottoms of ponds among the 
sediment and leaves, are from one eighth of an inch to 
nearly half an inch in length. Their bodies are flat, thin, 

64 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 



65 



-m 




and usually taper to the posterior end. They have two 

eyes on the upper surface of the body at 

the anterior end. It is of the parasitic 

flatworms that we wish especially to speak, 

namely, the flukeworm and tapeworm. 
Flukeworm. — This worm has a flattened, 

leaflike body (Fig. 29), from three fourths 

of an inch to two inches in length. It is 

parasitic in the livers of sheep and cattle, 

especially the former, and causes the dis- 
ease known as liver rot. It exists in 

this country, but is especially preva- 
lent in England, and causes the loss of 

many sheep there annually. The adult 

worm has two suckers at the anterior 

end of the body for attachment to its 

host. While in the liver of the sheep the 

worm lays great numbers of eggs which 

find their way to the intestines of the host and thence to 
the outside world. If an egg falls on 
damp herbage or in water there hatches 
from it a minute, ciliated embryo (Fig. 30). 
This embryo swims about in the water 
until it finds a certain species of snail. It 
then actually bores its way into the body 
of the snail, and after undergoing compli- 
cated changes transforms to an elongated 
body called a redia (Fig. 31). After a 
time, there are formed within the redia 
certain bodies called cercarice. Each cer- 
caria, which is provided with a long tail, 

eventually escapes from the redia and forces its way 



Fig. 29. — Liver 
flukewovm ; m, 
mouth ; r, re- 
productive 
opening; s, 
sucker. 




Fig. 30. — Embryo 
of flukeworm. 
After Thomas. 



herrick's zool. — 5 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 



out of the body 




Fig. 31. — Redia form 
of flukeworm as it 
appears in the body 
of the snail, show- 
ing cere arise. After 
Leuckart. 




Fig. 33. —Head of 

tapeworm showing 
suckers and hooks. 
Greatly enlarged. 



of the snail, crawls up the stem of a 
plant or blade of grass and secretes 
about itself a cyst or hard film of gela- 
tinelike substance. In these situations 
it is eaten by the grazing sheep. In the 
stomach of the sheep the cyst is dis- 
solved, and the imma- 
ture worm soon works 
its way to the liver, 
where it grows and be- 
comes mature, thus com- 
pleting the fife history. 
Tapeworm. — There 
are several species of 
tapeworms, all of which 
are parasitic in their 
adult stages, in the 
bodies of vertebrates, as, 
man, cattle, dog, sheep, 

birds, fishes, etc. At Fig. 32. — Cercaria 

least three different spe- 
cies are fairly common 
as parasites in the in- 
testines of man, but we 
shall speak of only one 
here, namely, the pork tapeworm. 1 

Like the flukeworm, the tapeworm 
passes the larval stage of its life history 
in one animal and the adult stage in 




form of flukeworm. 
In this form it 
escapes from the 
snail's body, climbs 
a blade of grass, and 
becomes encysted. 
After Leuckart. 



1 Dr. Charles Wardell Stiles says that the pork tapeworm is compara- 
tively rare in this country, and that the beef tapeworm is the most 
common one here. Bull. 19, U. S. Dept. Agri. B. A. I., 1898. 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 



67 



another animal. As seen in the mature stage in the diges- 
tive tract of man, the tapeworm has a head about the size 
of the head of a pin. The crown of this tiny head is beset 
with many minute hooks 
and the sides of the head 
are furnished with suckers 
(Fig. 33). All of these 
are for attachment to the 
host. The head is fol- 
lowed by a very short, 
slender neck. The body, 
from the neck on, has a 
jointed appearance owing 
to its being divided into 
jointlike divisions called 
proglottids. The body 
varies from twelve to 
twenty-four feet in length 
and from one quarter to 
two fifths of an inch in 
width, but is thin and 
tapelike, hence its name 
(Fig. 34). About half, 
and sometimes more, of 
the proglottids are ca- 
pable of producing eggs. 
When the terminal pro- 
glottid becomes gorged 

With eggS, it breaks away FlG> 34. -Adult tapeworm ; a, head. 

from the others and passes out of the host's body. The 
succeeding terminal proglottid, in time, does the same 
thing and is followed by others until many segments full 





68 FLATWORMS, ROUNDWORMS, AND ROTIFERS 

of mature eggs have been given off from the body. The 

eggs are carried away into ditches and waste places, where 

they may be eaten by pigs. The embryos 

soon hatch from the eggs in the intestines 

of the pigs, and immediately bore their 

way through the tissues to the muscles of 

the animal. In this situation the embryo 

changes into a flask-shaped form, known 

as the larva (Fig. 35). The presence of 

these larval tapeworms in the muscles of 

the pig give to the pork an appearance 

that causes it to be known as " measly 

pork." When such pork is eaten raw or 

insufficiently cooked, the larva? soon de- 

Fig. 35. — Larva velop into mature tapeworms in the di- 

of tapeworm. gestive tract of man. 

It is best to cook pork thoroughly before eating it, 

although tapeworms are not usually fatal to life. This rule 

of prevention also applies to the beef tapeworm. 

Roundworms 

On the whole the members of this group are more worm- 
like than the flatworms. Their bodies are, in general, 
cylindrical but unsegmented. Many of the roundworms 
are parasitic. Perhaps the small worms so often seen in 
strong vinegar and known as " vinegar eels" are the most 
familiar examples of the roundworms. The nematode 
worms that live in soil and attack the roots of certain plants, 
causing galls to form on the roots, are also more or less 
familiar. To this group also belong the so-called "hair 
worms," or "thread worms" (Fig. 36). These long slender 
worms are often found in drinking troughs and so much 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 



69 



resemble hairs that some people think they are transformed 
horse hairs. The guinea worm, which is a parasite of 
man in tropical countries and 
which sometimes attains a length 
of several feet, is a member of 
the group of roundworms. 

Trichinella spiralis. — This is 
one of the most important round- 
worms, economically speaking, in 
the United States. The adult 
worm is very small, scarcely vis- 
ible to the naked eye, and is 
found only in the intestines of 
mammals, as, man, pig, rat, etc. 
It is probable that the pig be- 
comes infested with this worm 
by eating the 

flesh Of Some Fig. 36. -Hair worm. 

animal, as the rat. Of course man be- 
comes infested by eating raw or half- 
cooked pork. In this way the worms, 
in a larval condition, are taken into the 
alimentary canal. There they soon be- 
come mature, and the young are produced 
in immense numbers. These soon work 
their way through the walls of the intes- 
tines and finally reach the muscles (Fig. 
37), where they become surrounded with 
a cyst, and there they remain. Before 
Fig. 37.— Trichinella forming the cyst, the embryos feed upon 
spiralis imbedded ^ e muscular tissue, causing serious com- 

in human muscle. ; ° 

After Leuckart. plications that of ten result in the death 





70 FLATWORMS, ROUNDWORMS, AND ROTIFERS 

of the host. The number of larvae that may be encysted, 
at one time, in the muscles of a human being is enormous. 
It has been estimated that, by eating an ounce of "trichi- 
nosed" pork not well cooked, eighty thousand worms might 
be set free in the intestines. 

Prevention. — Thoroughly cook every bit of pork eaten. 
If practicable, feed only vegetable products. If swill 
containing scraps of pork is fed to hogs, always cook it 
thoroughly before feeding. 

Rotifers, or Wheel Animalcules 

The third branch which we discuss in this chapter is 
represented by the miscroscopic animals known as roti- 
fers, or wheel animalcules. These interesting animals are 
abundant in fresh-water ponds, pools, puddles, and streams, 
and a few occur in the sea. They are almost sure to be 
met in aquaria. The majority are free-swimming, but a 
few are fixed in the adult state. Although these animals 
are microscopic they have distinct digestive and nervous 
systems and a complex body structure. 

Figure 38 shows the form and appearance of a rotifer 
common in fresh water ponds. The body has two regions 
— a broad portion, the trunk, which forms the greater 
part of the body, and a rather long, slender portion, 
the tail. The trunk is inclosed by a glassy, trans- 
parent cuticle. At the anterior end of the body is an 
organ known as the trochal disk. The edge of the disk is 
fringed with cilia, which by their peculiar motion give the 
appearance of a wheel rotating. This disk, with the cilia 
and apparent rotary motion, is a distinguishing feature of 
these animals and gives them their name, Rotifera. The 
anterior portion of the body may be withdrawn into the 



ROTIFERS 

glassy cuticle of the 
trunk, and the tail is 
freely movable and is 
often lashed from side 
to side with sudden 
jerks. 

Rotifers are re- 
markable in two 
respects. First, the 
female lays two kinds 
of eggs, — summer 
eggs and winter eggs. 
The former have thin 
shells, and the latter 
thick shells which pro- 
tect them from the 
cold. The second re- 
markable characteris- 
tic is, that the bodies 
of rotifers will shrivel 
and dry up during 
a drouth, but when 
again brought into 
the presence of mois- 
ture, even after three 
or four years, will re- 
vive. This accounts 
for the sudden ap- 
pearance, after a rain, 
of rotifers in ditches 
that have been dry 
for months. 




Fig. 38. — A rotifer ; c, trochal disk ; 
tr, trunk; t, tail. 



72 FLATWORMS, ROUNDWORMS, AND ROTIFERS 

Lamp Shells 

These animals are representatives of a class containing 
several widely different forms. The lamp shells resemble 
mollusks because their bodies are inclosed in bivalve shells. 
But the valves are dorsal and ventral, whereas the valves 
of the shells of a clam are right and left and similar. In 
many of these animals, the shells are shaped like an old 
Roman lamp, hence the name. 

They are all marine and many of them are attached to 
some object in the sea by a fleshy stalk, or peduncle. They 
are remarkable for the fact that their shells are found in 
nearly the oldest rocks in the earth and are very little 
different from the forms existing to-day. 

Relationships and noteworthy features of the worms. — 
The relationships of these animals are very uncertain. It 
is thought, with reason, that the foregoing groups of worms 
are most closely related to the ccelenterates, and so they 
closely follow in the scale of progression. 

One thing is preeminently characteristic of some of the 
worms, namely, the strange and remarkable changes they 
pass through in completing their life history, notably the 
liver fluke. Moreover, it will be recalled that part of the 
life history of certain worms is passed inside the body of 
one host and another part of the life history within the body 
of a second and very different host. Again, certain worms 
are able to live and thrive within the bodies of several 
different animals. Another noteworthy feature of many 
worms is that they are parasitic and cause certain malig- 
nant diseases when present in man. 

The worms are also well adapted to maintain themselves 
on the earth. Their ability to live in different hosts, in 



FLATWORMS, ROUNDWORMS, AND ROTIFERS 73 

Varied situations, and on water and land show this. Recall 
that the rotifers lay two kinds of eggs to meet different 
conditions and maintain an existence. 

Progression. — It is evident that the animals discussed 
in these four branches are more highly developed than those 
of the foregoing branch. Starting with the flatworms, we 
find that many of them have a rather complete digestive 
system and concentrated nervous system. The digestive 
system of the flukeworm consists of a mouth, pharynx, gul- 
let, and intestine, while the nervous system consists of a 
ring of nerve matter around the gullet which gives off a 
number of nerves, one pair running the length of the body. 
Trichinella has a mouth, pharynx, and intestine, with a ring 
of nerve matter about the pharynx that gives off nerves. 
The rotifers possess a mouth, pharynx, gullet, stomach, and 
intestine, — the most complete digestive system that we 
have seen so far. They also have a small brain. 

CLASSIFICATION OF THE EXAMPLES 

Branch IV — Platyhelminthes. 
Class — Trematoda. 

Order — Digenetica. 
Type of Order. 

Distomum hepaticum — Liver flukeworm. 
Class — Cestoda. 

Order — Polyzoa. 
Types of Order. 

Taenia solium — Pork tapeworm. 
Taenia saginata — Beef tapeworm. 
Branch V — Nemathelminthes. 
Class — Nematoda. 

Order — Nematoidea. 
Type of Order. 

Trichinella spiralis — Trichina. 



74 FLATWORMS, ROUNDWORMS, AND ROTIFERS 

Branch VI — Trochelminthes. 
Class — Rotifera. 

Order — Bdelloi'da. 
Type of Order. 

Rotifer citrinus — Wheel animalcule. 
Branch VII — Molluscoidea. 
Class — Brachiopoda. 
Order — Articulata. 
Types of Order. 
Various species. 



IX. EARTHWORMS, LEECHES, AND SEAWORMS 

Branch VIII. — Annulata (annulus, ring) 

Annulata. — With very few exceptions the members of 
this branch have their bodies divided externally into a 
number of rings which represent a division of the internal 
parts into a series of segments. The segmented worms 
are widely distributed. They are found on land, in fresh 
water, and in the sea. 

Example of the Branch — the Earthworm 

External features. — The body is long and cylindrical, 
bluntly pointed at one end and rounded and flattened at 
the other. The bluntly pointed end of itSv body which 
bears the mouth is known as the anterior end. The opposite 
end of the body is known as the posterior end. At the an- 
terior end of the body is a small lobe which overhangs 
the mouth and is called the prostomium, or "lip." A 
short distance back of the anterior end is a swollen ring, 
or band, called the clitellum. It is furnished with glands 
for secreting mucus to form the egg capsules. If a 
worm be carefully watched, it will be found that a certain 
side of the body is always held uppermost and away from 
the ground. This is called the dorsal side. The side of 
the body in contact with the ground is called the ventral 
side. Moreover, the body is plainly divided into rings,- or 
segments. The segments seem to be marked off by super- 

76 



76 



EARTHWORMS, LEECHES, AND SEAWORMS 



ficial wrinkles of the skin, but, in reality, a partition of thin 
tissue extends vertically through the body at every constric-. 
tion and divides the body internally into as many compart- 
ments as there are segments. 

Bilateral symmetry. — If, when the earthworm is in a 
natural position with the dorsal side uppermost, the body 
is cut lengthwise, exactly on the middle line, into two equal 
halves, the right half will be exactly similar to the left half. 
" This similarity is called two-sided likeness, or bilateral 
symmetry." It is a structure common to the higher animals 
and reaches its greatest perfection in the human body. 

The general plan of the body. — The body of the earth- 
worm is made up of two tubes, a small one within a con- 



Brain ganglion 4 ortic arches ' 




Gullet Crop Gizrsr,™c, I M) i Intestine • 

TTT^TN^f f fT I I I I II I I 



Vehtrq l bl ?$& vessel 



Ganglia '■ lOviduct^^^ 1 ^^^ organs 



Ovary 

Fig. 39. — Diagram of the internal structure of an earthworm. 

siderably larger one. The small, inner tube is the alimen- 
tary canal opening in front by the mouth and behind by 
the anus. The outer tube is formed by the body walls of 
the worm and since it is so much larger than the inner tube 
there is a space surrounding the alimentary canal but in- 
closed by the body walls. This space is known as the body 
cavity, or coelome. Here again we find a structure com- 
mon to the higher animals. Within the body of a sparrow 
or rabbit is a space surrounding the alimentary canal but 



EARTHWORMS, LEECHES, AND SEAWORMS 



77 



inclosed by the body walls that is termed the body cavity, 
or ccelome. In the earthworm, as we have already noted, 
the body cavity is divided into compartments by thin cross 
partitions (Fig. 39). 

Structure of the body walls. — The body walls of an earth- 
worm are made up of five distinct layers of tissue. The outer- 



Dorsal blood 
vessel 




Cuticle 

Epidermis 

Circular 
muscles 



ongitudinal 
muscles 



(Coelomic 
epithelium^ 



Ventral blood Nerve cord Setae 
vessel 

Fig. 40. — Diagram of a cross section of an earthworm. 



most layer is a thin, transparent membrane called the cuticle. 
Just beneath this is the skin, composed of long cells placed 
vertically to the surface of the body like the palisade cells 
of a plant leaf. Next to the skin is a layer of muscles that 
encircle the body, hence called circular muscles. Within 
this layer is one composed of muscles that run lengthwise 
of the body, therefore known as the longitudinal muscles. 
Lastly is a very thin layer of flat cells called the coelomic 
epithelium. This layer of cells lines the coelomic cavity. 



78 EARTHWORMS, LEECHES, AND SEAWORMS 

The notable thing about the body walls is the two layers 
of muscular tissue each composed of muscles running in 
opposite directions. The wriggling, crawling movements 
of this animal are produced by these two layers of muscles. 

The bristles, or setae of the earthworm. — The body of 
the earthworm is furnished with four double rows of stiff, 
chitinous bristles, or setae. They may be felt by drawing 
the worm backward across the hand. There is one double 
row along each edge of the ventral surface and one double 
row along the lower part of each side of the body (Fig. 40). 
Each segment, except the first two or three and last, 
has four pairs of setae and each pair is provided with mus- 
cles so that the bristles may be turned and held in various 
directions, and extended or withdrawn. When a bristle 
wears out, it is cast off and a new one grows in its place. 

Movement of the earthworm. — If an earthworm is placed 
on a piece of glass or other smooth surface, it will squirm 
and wiggle but will make no progress. It is capable of 
motion on a smooth surface but cannot change its location. 
This is because the setae, which perform an important func- 
tion in the locomotion of the animal, are unable to do their 
work on smooth surfaces. Under ordinary conditions the 
bristles stick into the soil and prevent the worm from slip- 
ping backward, when the muscles contract to force the body 
forward. On hard smooth surfaces the bristles are unable' 
to get a hold and the worm, - despite its struggles, re- 
mains in one place. When the worm desires to move for- 
ward, it points the setae backward and they stick into the 
soil. The longitudinal muscles, which are then contracted, 
pull the posterior end of the body forward and shorten and 
thicken the whole body. The circular muscles now con- 
tract, thus forcing the body to become thinner and longer. 



EARTHWORMS, LEECHES, AND SEAWORMS 



79 



But since the setae will not allow the body to slip backward, 
it is forced in a forward direction. By repeating these 
operations the worm 
progresses slowly from 
place to place. Very 
often the earthworm 
desires to travel back- 
ward, especially when 
it wishes to back 
quickly into its bur- 
row. In this case the 
setse are pointed for- 
ward and the same 
muscular contractions 
suffice for the back- 
ward movement. 

The digestive sys- 
tem. — The alimenta- 
ry canal runs straight 
through the body 
from end to end. It 
consists of several 
\ fairly distinct parts, 
each with its own pe- 
culiar function. The 
mouth is a simple, 
crescent-shaped open- 
ing at the anterior 
end of the body, and 
is overhung by the lip, or prostomium. This worm has no 
teeth nor tongue. Beginning at the mouth is the barrel- 
shaped pharynx, extending through several segments. 




Fig. 41. — Earthworm: 1, anterior end 
opened along dorsal side ; b, brain ; e, gullet ; 
t, seminal vesicles; c, crop; g, gizzard; 
bv, blood vessel; i, intestine; 2, anterior 
end ; m, mouth ; s, setae. 



80 EARTHWORMS, LEECHES, AND SEAWORMS 

Its walls are thick, muscular, and capable of contraction 
and expansion. Following the pharynx is the slender, 
thin-walled gullet which extends through eight segments 
to the crop, a short reservoir formed by a dilatation of the 
alimentary canal. Adjoining the crop is the gizzard, a 
firm, muscular organ lined with a chitinous membrane. 
The remaining part of the canal answers both as a stomach 
and intestine. It is a straight, thin-walled tube without 
glandular appendages such as the liver and pancreas found 
in the higher animals (Fig. 41). 

The process of digestion. — Digestion begins before the 
food even enters the mouth of the worm. A certain di- 
gestive fluid is poured forth from the mouth to moisten the 
food about to be eaten. It is thought that lime secretions 
from certain glands connected with the gullet mix with the 
food while passing through this organ and neutralize the 
acids produced by the leaves. The gizzard grinds the food 
and is usually aided in this work by fine sand. The main 
action of digestion goes on in the anterior part of the 
stomach-intestine . 

The circulation of the earthworm. — This animal possesses 
two circulations, the coelomic circulation and the vascular 
circulation, each being quite distinct from the other. The 
ccelome is filled with a colorless fluid which is driven to all 
parts of the body by contractions of the body walls. This 
fluid passes from one segment to another through holes in 
the thin cross-partitions. It is supposed that the nutritive 
portions of the food pass through the walls of the intestine 
into the coelomic fluid and are thus carried directly to all 
the organs which this fluid bathes. 

The blood, or vascular circulation is fairly well developed, 
for the blood is red and circulates through a system of 



EARTHWORMS, LEECHES, AND SEA WORMS 81 

closed tubes. The red coloring matter, hcemoglobin, is 
dissolved in the liquid itself and is not contained in cor- 
puscles as in the blood of mammals. The blood of the 
earthworm contains corpuscles, but they are colorless. 
Running along the dorsal side of the alimentary canal is 
a long, muscular tube that can be seen through the partly 
transparent skin of a living worm as a dark red band. 
This is the dorsal blood vessel. By close observation sue-! 
cessive wavelike contractions may be seen to pass rapidly 
from the posterior end of this tube forwards. Lying be- 
neath the alimentary canal is a similar tube, the ventral 
blood vessel, which carries the blood it receives from the 
anterior end of the dorsal vessel, posteriorly. There are 
also five pairs of short tubes that arch to the right and left 
around the gullet in the 7th, 8th, 9th, 10th, and 11th seg- 
ments. These tubes, the aortic arches, connect the dorsal 
vessel with the ventral vessel and since they are contractile 
are often called the " hearts" of the worm. Smaller tubes 
branch off from these main ones and extend to different 
parts of the body. 

How the earthworm breathes. — The earthworm has no 
lungs, gills, or other special organs of respiration. The thin 
walls of the moist skin are everywhere traversed by a net- 
work of minute blood vessels that lie just beneath the sur- 
face, so that they are separated from the air by only a very 
thin membrane. Oxygen is therefore easily absorbed from 
the air through all parts of the skin and conversely carbonic 
acicl gas is given off by the blood and passes outward through 
the skin. This is a very simple form of respiration, but 
answers admirably for such an elongated, thin-skinned 
animal. 

The excretory system. — As we have just explained, some 

herrick's zool. — 6 



82 



EARTHWORMS, LEECHES, AND SEAWORMS 



of the waste materials of the body are excreted through the 
skin in the form of carbon dioxide. But the principal 
organs of excretion are convoluted tubes, known as ne- 
phridia, a pair of which is found in each segment of the body 
except the first three or four and the last one. Each ne- 
phridium opens at one end to the exterior by a minute pore 
in the body walls between the upper and lower rows of setoe. 
The inner end of each nephridium has a funnel-shaped 
orifice lined with cilia that opens freely into the body cavity. 
These organs act as simple kidneys and carry off the waste 
matters of the body. 

The nervous system. — This animal has a brain composed 
of two ganglia on the dorsal side of the anterior part of 
the pharynx. From each ganglion of 
the brain a nerve cord passes down- 
ward on the corresponding side of the 
pharynx. These cords meet below. 
Thus the pharynx is completely en- 
circled by what is called the " nerve 
ring/' or " esophageal collar" (Fig. 
42). After the nerve cords meet they 
pass throughout the length of the 
worm on the floor of the body cavity 
and become so closely fused that they 
Fig. 42. - Anterior end of appear as a single cord. In each seg- 
earthworm : b, brain ; g, ment of the body both cords become 

ga,nglia. After Leuckart. ■, -, ■> r i i i v 

enlarged and form a double ganglion 
which appears as one. Smaller nerves pass from these 
ganglia to different parts of the body (Fig. 42). 

Senses of the earthworm. — It has been shown that all 
parts of the skin of the earthworm contain cells each of 
which gives off a nerve fiber that runs directly to the large 




EARTHWORMS, LEECHES, AND SEAWORMS 83 

nerve cord already described. This explains the fact that 
the sense of touch is well developed and extends over the 
whole surface of the body. It is thought that the sense of 
taste is located in the mouth and pharynx. Darwin has 
shown that the sense of sight, feeble though it is, is con- 
fined chiefly to the anterior end of the body, although the 
posterior end is sensitive to light. It is certain that the 
earthworm perceives the difference between darkness and 
light for it withdraws to its burrow during the daytime, and 
when a bright light is flashed upon the anterior end, it con- 
tracts. It has no eyes, and we have no reason to suppose 
that it is capable of forming pictures of objects. Neither 
is there evidence to show any sense of hearing. 

Its food and how eaten. — The food of the earthworm 
comprises both animal and vegetable matter, the latter 
consisting largely of bits of leaves. Besides these articles 
of food it swallows large quantities of earth that pass slowly 
through the alimentary canal, during which passage the 
nutritive portions contained in it are absorbed and digested. 
This earth is usually obtained at a considerable depth, but 
the waste parts of it thrown off by the alimentary canal are 
deposited at the surface of the ground and form the so- 
called " castings" about the mouths of their burrows. 

The pharynx is muscular and contractile. Moreover, 
muscles run from the outside of the walls of the pharynx 
to the inside of the body walls. These expand- the pharynx, 
and if the mouth has been previously applied to any solid 
object, such as a leaf or pebble, the pharynx acts upon it 
like a suction pump and draws it into the alimentary 
canal if desired. 

Regeneration of lost parts. — Earthworms are remarkable 
for their ability to withstand injury and to regenerate lost 



84 EARTHWORMS, LEECHES, AND SEAWORMS 

parts. If one be cut in two pieces, each portion, under 
favorable conditions, is capable of reproducing the lost 
part with its organs, thus producing two complete worms. 
Moreover, the anterior half of one worm may be success- 
fully grafted on to the posterior half of another. 

Its life history. — Each earthworm produces both sperms 
and ova, but the ova are fertilized by the sperms from a 
different individual. About the time the eggs are ready 
to be laid, a band, or collar, is formed around the clitellum 
from mucus secreted by the glands of this organ. The 
collar, which is gradually slipped forward, receives the ova 
and sperms as it passes along and is finally worked off 
over the anterior end of the worm. The collar now be- 
comes closed at both ends and forms a horny capsule 
containing the eggs. These capsules are deposited in 
loose earth, or under logs and stones, where they re- 
main until the young worms emerge. Some of the eggs 
in each capsule do not hatch but remain to furnish food 
for the young worms produced from the other eggs. 

The distribution and habits of earthworms. — There are 
many kinds of earthworms and they are found in all parts 
of the world. They live in the earth in burrows varying in 
depth from a few inches to several feet. They are noctur- 
nal animals and spend the day hidden in their burrows 
with the head lying near the surface if the ground is moist. 
At night they come out in search of food, but usually remain 
with the posterior end attached at the mouth of the burrow, 
ready to disappear if danger threatens. They gather up 
bits of leaves for food and collect pebbles to line the upper 
parts of their burrows and to stop up the entrances after 
withdrawing the body. As the ground becomes dry in 
summer they burrow deeper and deeper into the soil and 



.EARTHWORMS, LEECHES, AND SEA WORMS 85 

seldom appear on the surface unless it rains. In winter 
they hibernate below frost line. 

The economic importance of earthworms. — Mr. Darwin 
has shown that earthworms exercise a profound influence 
upon the surface soil. They are constantly depositing their 
" castings" upon the surface of the ground near the mouths 
of their burrows. This earth has been brought from con- 
siderable depths and carries whatever fertilizing constituents 
there may be at these depths below the reach of the roots 
of ordinary plants. Moreover, the earth, in passing through 
the alimentary canal of the worm has been worked over 
and its fertility increased. Therefore, earthworms may be 
looked upon, in general, as improvers of the soil. Darwin 
estimated that, if the castings of earthworms were spread 
uniformly over the surface of England, they would add two 
tenths of an inch every year to the thickness of the rich 
surface soil. 

Leeches. — In many of our streams, lakes, swamps, and 
marshy places there exist segmented, half-parasitic worms, 
known as leeches, or " blood-suckers." Their bodies are 
somewhat flattened and in some species, at least, are capable 
of great distention. The bodies of most leeches have a 
sucking disk at both the anterior and posterior ends. By 
means of these suckers they cling firmly to the bodies of 
other animals. Sometimes the mouth is furnished with 
teeth and sometimes not. In some leeches the capacity 
of the crop is greatly increased by a series of pouches placed 
along the sides of the crop and communicating with it. In 
this way the crop is able to hold a supply of food sufficient 
to last the leech several months. 

In the olden times it was the custom, among physi- 
cians, to " bleed" patients. For this purpose leeches were 



86 EARTHWORMS, LEECHES, AND SEAWORMS 

employed, because they produced scarcely any pain, 
while sucking the blood. These worms are occasionally 
used for this purpose yet and are found for sale in some 
drug stores. Leeches are raised in France on a commer- 
cial scale. Swamps are stocked with them, and they 
are then fed on worn-out horses, cattle, etc. 

Certain leeches, in India, that live on the land are great 
pests to the natives and domestic animals. Others are 
parasites, clinging to the bodies of fish, and one, the horse- 
leech, is sometimes parasitic in the throats of horses and 
cattle. Some are carnivorous, living on the bodies of 
snails and other mollusks. The eggs of leeches are usually 
inclosed in cocoons. 

Sea worms. — There are many worms living in the sea. 
Some are free-swimming ; some crawl along the bottom ; 
some live in burrows, and some in tubes. Perhaps the 
majority of marine worms are found in shallow water along 
the shores of the sea, although some have been dredged 
from depths of over three thousand fathoms. 

The tube-building sea worms are interesting creatures. 
Most of them lead a sedentary or fixed life. The tubes of 
some are formed from hardened mucus secreted by special 
glands of the body. Others make their tubes from grains 
of sand or mud or even from fragments of shells stuck to- 
gether with mucus. A few are free and actually carry 
their tubes about with them. 

Progression. — The earthworm and leech are probably 
the highest animals we have met so far. In the first place 
the bodies of both are truly segmented. That is, the cavity 
between the alimentary canal and the body walls, known as 
the coelome, is divided into compartments by cross-parti- 
tions. Bear in mind that they are the first animals we have 



EARTHWORMS, LEECHES, AND SEA WORMS 87 

met with segmented bodies. Moreover, these animals 
have a double nerve running throughout the whole length 
of the bod)' and a distinct brain. Correlated with the 
brain, as we should expect, are eyes, at least, in some of 
the leeches and seaworms. 

Adaptations to mode of living. — The home of the earth- 
worm is in the soil. It burrows all through the soil in 
search of its food. The food is derived largely from 
quantities of soil, which are passed straight through the 
alimentary canal. To facilitate the passage of such a 
quantity of useless material the alimentary canal is 
straight. At the same time there must be a large amount 
of absorbing surface in the canal to take up the food 
contained in the soil, while it is passing through. To 
provide such a surface and yet not have the canal coiled, 
the body must be long, and so it is. More than this, the 
shape of the body is most economical for a burrowing 
animal without strong jaws or claws. That is, if the body 
of the worm were short and thick, a larger hole would have 
to be made and, consequently, more digging done. Again 
there are many setse on the ventral side of the body which aid 
greatly in crawling up the sides of the burrow. 

The leech is furnished with suckers, which certainly 
adapt it to its mode of life. Moreover, the crop is some- 
times enlarged by lateral pouches, that it may hold suffi- 
cient food to last the animal for a long time. Finally, the 
body can be greatly distended to provide room for the 
storage of food. Undoubtedly leeches often go several 
weeks without finding an animal whose blood may be 
drawn. If it were not for the enlarged crop and extensible 
body, in which the blood can be stored to tide over the in- 
tervals when no food is obtainable, the animal might die. 



88 EARTHWORMS, LEECHES, AND SEA WORMS 

CLASSIFICATION OF THE EXAMPLES 

Branch VIII — Annulata. 
Class — Chsetopoda. 
Type of the Class. 

Lumbricus agricola — Earthworm. 
Class — Hirudinea. 
Types of the Class. 

Hirudo medicinalis — Medicinal leech. 
Hwmopis vorax — Horse-leech. 
Macrobdella decora — American leech. 



X. STARFISH, SEA URCHIN, BRITTLE STARS 

Branch IX. — Echinoderinata (echinos (spine), hedge- 
hog; derma, skin) 

Most of the members of this branch have the surface of 
the body beset with spines; hence the name, Echinoder- 
mata, meaning spiny skins! In all the echinoderms the parts 
of the body are arranged in a radial manner. In nearly 
all there is an exoskeleton composed of calcareous plates. 
Without exception they are found in the sea. 



An Example of the Branch — the Starfish 

The form and radial symmetry of the starfish. — The 

common starfish has a star-shaped body consisting of a 
central portion known as 
the central disk, and five 
tapering arms. The arms 
radiate from the central disk 
much as the spokes of a 
wheel radiate from the hub. 
This radial arrangement is 
characteristic of all mem- 
bers of this branch and is 
known as radial symmetry 
(Fig. 43). 

External features. — In its natural position, one side 
of the body is always uppermost. This side is called the 

89 




Fig. 43. 



Ventral surface of a 
starfish. 



90 STARFISH, SEA URCHIN, BRITTLE STARS 

aboral surface. The opposite side is called the oral sur- 
face (Fig. 43). In the center of the oral surface is an 
opening, the mouth. Radiating from the mouth are five 
grooves, one along the median line of the oral side of 
each arm. These are the ambulacral grooves. The 
whole body is beset with many stiff spines. Bordering 
each of the ambulacral grooves there are two or three 
rows of spines that are movable. These are the ambulacral 
spines. On the aboral surface, between the bases of two 
arms, is a small circular .plate, the madreporite, which is 
marked by a number of fine, straight, or wavy ridges and 
perforated with many minute openings. 

The tube feet. — In each of the ambulacral grooves there 
are two double rows of soft, flexible, and cylindrical bodies, 
the tube feet. Each tube foot is a hollow cylinder, ends with 
a sucker, and can be greatly extended or contracted. These 
are the organs of locomotion. 

Structure of the body walls. — The body walls consist 
of three layers: an outside layer of thin epidermis that 
covers the whole body; a middle and much thicker layer, 
the mesoderm, and a delicate inner layer, the coslomic epithe- 
lium. The latter not only lines the whole body cavity, 
but forms an outside covering for the internal organs. 

Skeleton. — The body of the starfish is inclosed in a 
hard, rough integument, the skeleton, consisting of many 
small, irregular, calcareous plates, termed ossicles. The 
ossicles are loosely joined together by a connective tissue 
so that the skeleton is more or less flexible and a certain 
amount of movement is permitted. The skeleton is be- 
neath the epidermis and is developed from the mesoderm. 

In the spaces between the ossicles, on the dorsal surface, 
there are several minute pores in the connective tissues. 



STARFISH, SEA URCHIN, BRITTLE STARS 



91 



Through these openings, very small, soft, fringelike pro- 
jections of the inner body-lining protrude. These are 
the branchice. 

The digestive system of the starfish. — The mouth opens 
into a short gullet that leads to a five-lobed sac, the stomach. 
The stomach is large, thin-walled, and very extensible. 
It is divided into two portions by a constriction in the 
middle. The lower part is called the cardiac portion, and 
the upper part is 
called the pyloric por- 
tion. The pyloric di- 
vision opens into a 
short intestine that 
leads to a very small 
anal aperture on the 
dorsal side of the 
body. 

Nearly filling the 
cavity of each arm is 
a pair of long, brown- 
ish appendages, the 
pyloric cceca (Fig. 44) . 
The pyloric cseca have 
glandular walls, and 
as they secrete a digestive fluid are to be looked upon 
as digestive glands. Each pair is connected by a single 
tube with the pyloric division of the stomach and empties 
its secretions into this part of the stomach. 

The food of the starfish and how eaten. — The starfish 
lives upon crustaceans and mollusks, especially oysters. 
When a starfish attacks an oyster, its body is arched over 
the latter, and the stomach is extruded through the mouth 




Fig. 44. — Upper walls of a starfish cut away 
to show the pyloric caeca, or hepatic lobes. 



92 



STARFISH, SEA URCHIN, BRITTLE STARS 



and wrapped around the victim, which is then dissolved 
and digested, after which the stomach is withdrawn into 
the body. 

The water vascular system. — The madreporite, of which 
we have already spoken, is the cover to a short canal, the 
stone canal, that runs downward and opens into a ringlike 
canal that encircles the mouth. Five long canals, one for 

each arm, radiate 
from the ring canal 
about the mouth. 
Each of these long 
radiating canals is 
provided with many 
short side branches 
to which are at- 
tached the tube feet 
(Fig. 45). Each tube 
foot is connected, by 
a slender tube that 
passes through a 
minute pore between 
the ossicles, with a water bulb in the body cavity. The 
bulb and the tube foot are both contractile. 

This whole system of tubes is called the water vascular 
system (Fig. 45). The tubes are filled with a watery fluid 
composed largely of sea water that flows in through the 
madreporite. 

Locomotion of the starfish. — When the starfish desires 
to move, it compresses the water bulb connected with each 
tube foot and forces the water out into the latter organ. 
This greatly elongates each tube foot which is then directed 
forward in the direction the animal wishes to go. After 







Fig. 45. — Diagram of the water vascular sys- 
tem of a starfish : S, stone canal ; G, circular 
canal ; R, radial canal ; T, tube feet ; A, am- 
pullae. After Brooks. 



STARFISH, SEA URCHIN, BRITTLE STARS 93 

being stretched its full length, each tube foot is fastened to 
some object by the sucker at the end. Then all the tube 
feet are contracted and the body drawn forward. By a 
repetition of these acts the starfish progresses over the sur- 
face upon which it lies. 

The ccelome, or body cavity. — All of the large space 
within the central disk and arms and between the alimen- 
tary canal and body walls is called the ccelome, or body 
cavity. It is filled with a fluid that consists mainly of sea 
water but has numbers of amcebalike cells floating in it. 
This coelomic fluid is kept in motion by the cilia lining the 
ccelomic epithelium and thus constitutes a sort of circula- 
tion. The nutritive portions of the food are probably 
absorbed through the walls of the stomach directly into 
this fluid and are thereby carried to different parts of the 
body. 

How the starfish breathes. — We have already described 
the branchiae that project through openings between the 
ossicles on the dorsal surface. These are now supposed 
to act like gills in gathering the oxygen from the sea water 
and are thought to aerate the coelomic fluid which, in turn, 
probably carries fresh oxygen to all the organs it bathes. 

Nervous system. — Surrounding the mouth is a five- 
angled nerve ring, from which radiate five nerves, one for 
each arm. Each of the radial nerves runs along the bot- 
tom of an ambulacra! groove and may be seen by parting 
the tube feet along the middle line. At the extreme end 
of each of the ambulacral grooves is a small, bright red spot, 
the eye. Over each eye is an organ that resembles a tube 
foot without a terminal sucker. These organs are called 
tentacles and have been shown to be organs of smell. 

Life history and reproduction. — The starfish reproduces 



94 



STARFISH, SEA URCHIN, BRITTLE STARS 



by eggs and the sexes are separate. The ovaries of the 
female are within the body cavity at the bases of the arms. 
There is one pair for each arm. The spermaries of the 
male are in a similar situation. When the ova are mature, 
they are extruded into the sea through small pores in the 
body walls at the bases of the arms. In the sea they are 
fertilized by the sperms and finally hatch into forms very 
different from the adults. It is also an interesting fact 
that the young are bilaterally symmetrical. The young 
feed on microscopic organisms and, as they grow, undergo 
radical changes until finally they assume the form of the 
parent starfish. 

Other Echinoderms 

Not all starfish have just five arms. Indeed, abnormal 
specimens of the common starfish are sometimes found 
with four or six arms. But there are some species that 

normally have more than 
five arms. One species 
has as many as thirty. 
Again, the members of 
one genus have six arms, 
an irregular number. 
Not all starfish are like 
the- one described in 
regard to the central 
disk. In some, the disk 
is more plainly marked 
off and is more distinct, 
while in others the 

Fig. 46. -Ventral surface of a kind of star- between the 

fish in which the disk extends much farther ^ 

out than in the common starfish. arms are filled up nearly 




STARFISH, SEA URCHIN, BRITTLE STARS 



96 



to the tips, and it is difficult to tell where the disk stops 
(Fig. 46). 

Brittle stars. — These are starfish that are at once dis- 
tinguished from those above, by the long, slender, tapering, 
and cylindrical arms. The central disk is also more sharply 
marked off from the arms (Fig. 47). Again, there are no 
grooves along the oral 
surfaces of the arms, and 
the tube feet protrude 
through the sides of the 
arms instead of through 
the ventral walls, and are 
not provided with suck- 
ers. Hence, locomotion 
is effected largely by the 
slender arms. In some 
species of brittle stars, 
the basket stars, the arms 
are branched many times, 
producing a complex but 
beautiful object. Some 
brittle stars have the remarkable property of being able 
! to throw off pieces of their arms when touched or irri- 
jtated; hence the name, brittle stars. 

Sea urchins. — Sea urchins are common along the eastern 
coast of the United States, especially where the shore is 
rocky. They are globular in shape, but with the side, on 
which the mouth is situated, flattened. These echinoderms 
have no distinct arms, but the body is bristling with cylin- 
drical, pointed spines jointed to the skeleton so that they are 
movable (Fig. 48). There are also projecting among the 
spines, five double rows of tube feet radiating from the 




Fig. 47. — Brittle starfish. Note that 
the disk is clearly defined. 



96 



STAKFISH, SEA URCHIN, BRITTLE STARS 



mouth. On removing the spines and skin, a beautiful 
globular shell (Fig. 49) is exposed, within which are the 
organs of the body. The shell is composed of limestone 
plates which fit very closely together and are ornamented on 
the surface, with rounded protuberances, for the articula- 
tion of the spines. The plates composing the shell are 
grouped together in such a manner that they form ten dis- 




Fig. 48. — Sea urchin, showing spines on outside of shell. 



tinct zones. Five of these zones bear tube feet and five 
bear none, and each zone alternates with the other. There- 
fore, although the sea urchin does not possess five distinct 
arms bearing tube feet, yet the shell presents five distinct 
areas bearing tube feet, which is comparable with the 
structure of the starfish. The sea urchin possesses five 
long, curved teeth which lie mostly within the body, only 
the points projecting. 



STARFISH, SEA URCHIN, BRITTLE STARS 



97 




Fig. 49. — Shell of a sea urchin after spines have been removed. 



Certain sea urchins, such as the sand dollars, or sea 
biscuits (Fig. 50), have flat bodies, instead of globular ones. 
The bodies of others are soft and flexible, wholly unlike 
that of the common 
sea urchin. 

Sea cucumbers. — 
Superficially, these 
echinoclerms show 
little resemblance to 
a starfish or sea 
urchin. They are 
more or less cylindri- 
cal in shape and some 
of them roughly re- 
semble cucumbers in 
appearance. Some of 
them have five double 

herrick's zool. — 7 




Fig. 50. — Sand dollar, or sea biscuit* 



98 



STARFISH, SEA URCHIN, BRITTLE STARS 



rows of tube feet, and some of them have none. In 
some there is a distinct ventral side, and in others there 
is not. They do not have large and closely connected cal- 
careous plates in the body walls to form a continuous skele- 




Fig. 51. — Sea cucumber. Note the branched tentacles about the mouth. 

ton like that of the starfish and sea urchin, yet their bodies 
retain a cylindrical shape owing to many very small, loosely 
connected calcareous plates imbedded in the integument, 
somewhat like the spicules in the walls of a sponge. The 
body walls, notwithstanding, are leathery and flexible. 



STARFISH, SEA URCHIN, BRITTLE STARS 



A characteristic feature of the sea cucumbers is the much- 
branched tentacles about the mouth (Fig. 51). The 
tentacles vary in number from eight to twenty and some- 
times more. These are supposed to be much-modified 
tube feet, and are used to push food into the mouth. When 
the animal is disturbed, they can be 
greatly contracted and drawn completely 
back within the mouth. 

Sea cucumbers vary from two to fifteen 
inches in length, depending upon the 
species and the age of the individual. 
One species of Cucumaria sometimes 
attains a length of three feet and is 
orange-red in color. 

Feather stars. — This group of echino- 
derms comprises the lowest representa- 
tives and at the same time the oldest 
members of the branch. The feather 
stars, crinoids, or sea lilies as they are 
variously called, are found as fossils in 
the rocks of the paleozoic age and were 
very abundant in the past. The living 
forms are few and, for the most part, 
inhabit the deeper regions of the sea. It 
is a characteristic of the crinoids that 
they are attached to objects in the sea, FlG - 52 - ~" Sea lily - 
either for a short period of their life, or permanently. 
Most of the species are permanently attached to submarine 
objects by a stem, which frequently is very long, and 
made up of a series of joints perforated by a central canal. 
The body (Fig. 52), borne on the end of the stalk, has the 
oral side uppermost, which position, it will be recalled, is 




100 STARFISH, SEA URCHIN, BRITTLE STARS 

exactly the reverse of that in the starfish. The arms of the 
crinoids are often many times branched and the branches 
bear short, lateral projections called pinnulse that serve to 
give the animal a feathery appearance. 

Reproduction and development. — The echinoderms re- 
produce by eggs, not by budding, and the sexes are separate 
in the majority of species. In one species, at least, the 
female may be distinguished from the male by a difference 
in color. In this case the female is decidedly bluish in 
color while the male is reddish brown and presents a 
marked contrast to the former sex. The eggs and sperm 
cells are extruded into the water and there the sperm cells 
find the eggs and fertilize them. The egg then hatches 
into a tiny organism, the larva, which has cilia, is free- 
swimming, and in no way resembles the adult. The larvae 
of these animals pass through remarkable changes in 
their growth to adults and when first discovered, were 
thought to be distinct species of marine animals and 
were given various names. For example, the larvse of 
sea urchins and brittle stars were called Pluteus, while the 
larvae of the starfish were called Brachiolaria and Bipin- 
naria. 

Regeneration of lost parts. — Like the hydra, many of 
the echinoderms are remarkable for their ability to repro- 
duce parts of the body that may have been broken or thrown 
off. Certain of the starfish and many brittle stars, when 
molested, will throw off pieces of their arms or sometimes 
all of their arms. Indeed it is difficult to obtain these par- 
ticular species whole. Under these conditions the central 
disk will produce new arms and sometimes an arm will 
produce a new central disk and the other arms. Stranger 
still, in some sea cucumbers a part or even all of the ali* 



STARFISH, SEA URCHIN, BRITTLE STARS 101 

mentary canal is occasionally ejected from the body and 
in some cases, at least, becomes completely renewed. 

Economic importance of the echinoderms. — In the past 
starfish have caused much annoyance to oystermen because 
of the large numbers of oysters devoured by these echino- 
derms for food. Of late years, however, the oystermen have 
learned how to keep the oyster beds free, in a measure, 
from these pests. 

Certain species of sea cucumbers are used as food by the 
Chinese. Great numbers of them are caught on the coral 
reefs of the Pacific Ocean and China Sea and sold in Chinese 
ports under the trade name of " trepang." 

Relationships and characteristics of the echinoderms. — 
The echinoderms stand almost alone and without any near 
relatives. They all have an alimentary canal separate from 
the body cavity and a well-developed nervous system which 
place them above all animals so far studied. Without 
exception they live in the sea, and in all, the parts of the 
body are radially arranged. Moreover, the parts occur to 
the number of five or are repeated in multiples of five. 
This characteristic is well shown by the common starfish 
which has five arms and by the species of starfish that 
has thirty arms. Again, the members of this branch 
possess a water-vascular system and this is eminently 
(characteristic, for no other branch of animals is found 
with this structure. Unlike the ccelenterates, the echino- 
derms show no tendency to bud and form colonies of zooids 
and the great majority of them are free. They also 
possess an exoskeleton, which, in some, consists of plates 
joined together continuously and in others of scattered 
plates imbedded in the skin. In many the body is armed 
with spines, hence the name of the branch. 



102 STARFISH, SEA URCHIN, BRITTLE STARS 

CLASSIFICATION OF THE EXAMPLES 

Branch IX — Echinodermata. 
Class — Asteroidea. 

Order — Cryptozonia. 
Type of Order. 

Asterias vulgaris — Starfish. 
Class — Ophiuroidea. 
Order — Ophiurida. 
Type of Order. 

Ophioglypha lacertosa — Brittle star. 
Class — Echinoidea. 
Order — Regularia. 
Type of Order. 

Echinus drocbachiensis — Sea urchin. 
Class — Holothuroidea. 
Order — Pedata. 
Type of Order. 

Cucumaria frondosa — Sea cucumber 
Class — Crinoidea. 

Order — Neo-crinoidea. 
Types of Order. 

Antedon tenella — Feather star. 
Rhizocrinus lofotensis — Sea lily. 



XL MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 

Branch X. — Mollusca (mollis, soft) 

The mollusks are very widely distributed and some of 
them form an important source of food supply. They are 
found in the sea, on the land, and in fresh water. Most 
of them possess very soft bodies which are, in the major- 
ity of cases, protected by shells of carbonate of lime. 
Although the branch, Mollusca, is divided into several 
classes, we shall discuss only those containing the more 
familiar forms, represented by the clam, snail, and squid 
respectively. 

An Example of the Branch — the River Mussel 

The external features and structure of the shell. — The 
shell of the mussel is composed of two similar, right and 
left pieces, or valves. In its natural position, the shell 
is held vertically with the thin, or ventral edges buried 
in the mud and the broad, or dorsal edges up. The 
dorsal edges are joined for some distance by an elastic 
band, or ligament, the hinge ligament. The broad round 
end of the shell is anterior and the more pointed end is 
posterior (Fig. 53). Between the dorsal edges of the valves 
are the projecting hinge teeth that interlock with one an- 
other. On each valve, toward the anterior end, is a promi- 
nent elevation, the umbo, which is the oldest portion of the 
shell. Additions, marked by concentric rings, have been 

103 



104 MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 



made to the ventral edges of the umbo. The shell, which 
is a calcareous secretion of the outer layer of the mantle, 
is made up of three layer's. The outer layer is a horny, 



Hinge ligament 

rr _ Dorsal margin 

Umbo o/i****^^^ 
beak* 



greenish epidermis. 
The inner layer con- 
sists of thin, flat leaves 
of pearl, the fine sinu- 
ous edges of which 
produce an iridescent 
effect. The dark mid- 
dle layer consists of 
many-sided prisms 
placed at right angles 
to the surface of the 
shell. 

Internal features of the shell. — When the body of the 
mussel has been removed from the shell and all parts care- 
fully scraped away, 



Anterior 
end 




ostenor 
end 



Ventral 
\j margin 
Lines of growth 

Fig. 53. — Left valve of a clam shell 



Hinge 
tooth 



Lateral 

hinge 

tooih 



Posterior 

retractor 

muscle Posterim * 
adductor 
muscle 



each valve will pre- 
sent the following 
features: at the an- 
terior end of the 
shell the scar of the 
anterior adductor mus- 
cle will be seen; at 
the posterior end, in 
a similar position, 
is the scar of the 
large posterior ad- 
ductor muscle; in close connection with the anterior ad- 
ductor muscle, are two smaller scars, the upper one, the 
scar of the anterior retractor foot muscle, and the lower, 




Fig. 54. — Right valve of a clam shell. 



MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 105 



Liyature 



the scar of the protractor muscle of the foot; just above the 
posterior adductor muscle scar is the small scar of the 
posterior retractor foot muscle; parallel with the edge of 
the valve and a short distance from it is a delicate streak, 
the pallial line, that marks the line along which the 
mantle lobe is joined to the shell (Fig. 54). 

How the mussel opens and shuts its shell. — The anterior 
adductor muscle and the posterior adductor muscle run 
straight across the cavity between 
the valves, and their ends are 
fastened firmly to the inside walls 
of the shell (Fig. 55). Therefore, 
when they contract and shorten, 
the valves are pulled together 
and held tightly closed. On the 
other hand, whenever the ad- 
ductor muscles are relaxed, the 
strong hinge ligament, which all 
the time the valves are closed is 
tightly stretched, throws the shell 
open by its elasticity. Thus the 
shell is closed with muscular 
effort, but is opened by a me- 
chanical, springlike action which 
requires no effort on the part of the animal 
is open much more than it is shut, this is a striking adap- 
tation to the mussel's mode of living. 

The mantle and siphons. — Lining the inside of both 
valves and completely enveloping the body is a soft, white, 
delicate membrane known as the mantle. It really consists 
of two lobes corresponding to the valves. The ventral 
edges of the mantle lobes are free and run parallel with the 




Fig. 55. —Cross section of mus- 
sel, showing mechanism of 
opening and closing. 

Since the shell 



106 MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 



Exhalent siphon 



Inhalent 
siphon 



edges of the valves, but the mantle is fastened, a little way 
from the edge, to each half of the shell along the pallial 
line, already noted. At the posterior end of the shell 
the mantle forms two short tubes, the siphons, which pro- 
ject between the edges of the valves when the mussel rests 
undisturbed (Fig. 56). In this position a current of water 
is always passing in through the lower, or inhalent siphon, 

and out through the 
upper, or exhalent siphon 
(Fig. 56). 

The gills and respira- 
tion. — On either side of 
the posterior part of the 
body, inside the mantle, 
is a pair of gills. They 
hang suspended with the 
lower edges free and pre- 
sent a ribbed, or striated 
appearance. Each gill has 
the form of a long narrow 
bag or trough open above 
and divided into compart- 
ments by cross-partitions. 
In addition, the sides of 
the bag, or gill, are per- 
forated with many small, 
ciliated openings through 
which the water flows. 
Moreover, canals run up 
and down inside of the 
thin walls of the gills for conveying the blood (Fig. 56, B). 
The outer walls of the outer gills are attached to the 




Mouth 



Blood 



Water 




Fig. 56. 



Diagram of a clam and portion 
of a gill. 



MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 107 



Intestine 



mantle lobes along the entire length of their dorsal edges, 
and the inner walls of the inner gills are attached to the 
sides of the body (Fig. 57). Thus the mantle cavity is 
divided into two chambers : a dorsal, or cloacal chamber and 
a ventral, or branchial chamber. The fresh sea water 
carrying oxygen is brought into the branchial chamber 
through the inhalent siphon (Fig. 56). The gill cilia then 
cause it to flow through the 
holes in the sides of the gills 
into the troughs of these 
organs, whence it passes into 
the cloacal chamber and out 
through the exhalent siphon. 
The blood in the gills is sepa- 
rated from the surrounding 
water by the very thin, mem- 
branous walls of the gills, 
and the carbon dioxide read- 
ily passes through this tissue 
by osmosis, and the oxygen 
is readily absorbed from the 
water in exchange. 

The foot and locomotion. — 
At the anterior end of a living mussel a white, flexible, 
muscular organ, the foot (Fig. 58), is often seen protruding 
forward and downward between the gaping ventral edges 
of the shell. This is the organ of locomotion. In its nat- 
ural position the mussel stands with the anterior end of 
the shell considerably deeper in the mud than the posterior 
end. This leaves the siphons clear of the mud and in direct 
communication with the water above. In this position the 
mussel plows slowly along through the mud. The foot is 




Fig. 57. — Cross section of clam. 



108 MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 



slowly extended outward and downward into the mud and 
anchored there. Then the retractor muscles contract and 
pull the shell and body up to the foot, as it were. By a 
repetition of these movements of the foot the mussel covers 
considerable distances in the course of time. 

The alimentary canal and digestion. — The mouth is 
just under the anterior adductor muscle and between two 
pairs of soft flaps, the labial palps. It leads by a short 
gullet to the spherical stomach, which is surrounded by a 

dark green mass, the 
Posterior adductor muscle^ digestive gland, or 
Digestive gto™^j% ar t \ -liver." The in- 
^JJreterj testine passes down- 

A^^^/}^^^^^^^] ward from the stom - 

ach, coils once or 

twice in the abdo- 
men and foot, and 
returning, runs pos- 
teriorly through the 
ventricle of the heart 

Fig. 58. — Internal structure of a clam. anc J enc J s ^ ac k f the 

posterior adductor muscle (Fig. 58). The food, which con- 
sists of minute plant and animal organisms, is brought in 
by the inhalent current, carried to the anterior end of the 
body (Fig. 56), and directed into the mouth by the cilia of 
the labial palps. It is acted upon by the fluids from the 
digestive gland and is absorbed from the stomach and 
intestine. 

Excretory organs. — The excretory organs consist of a 
pair of dark-colored kidneys lying just below the pericar- 
dium and in front of the posterior adductor muscle (Fig. 
58). Each kidney consists of a glandular portion, the 




MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 



109 



kidney proper, and the urinary tube. The whole organ has 
two openings, one of which opens into the cavity of the 
pericardium or sac around the heart while the other opens 
on the side of the abdomen near the base of the inner gill. 
It is from the latter that the excretions of the kidneys are 
carried away by the current of water through the exhalent 
siphon. 

The heart and circulation. — The heart is situated in the 
dorsal part of the body just below the hinge ligament and 
is surrounded by a membranous sac, the pericardium. It 
consists of one ventricle and a right and left auricle. Two 
arteries arise from the ventricle, one from the anterior end 
which passes above the intestine and conveys the blood to the 
forward parts of the body and another from the posterior 
end which rims below the intestine and carries blood to the 
posterior part of the body. By the contractions of the 
heart the blood is sent out through the arteries into irreg- 
ular channels that 
reach all parts of the 
animal. On its re- 
turn the blood passes 
first through the kid- 
neys, where it gives 
up nitrogenous waste 
matters. Then it 
flows to the gills, 
where it is aerated, 

and finallv from the Fig. 59. — Part of nervous system of a clam. 

gills, it passes directly into the thin-walled auricles. These 
open into the ventricle. Thus the blood reaches its start- 
ing point, having completed the circuit of the body. 

The nervous system. — This system consists of three pairs 




110 MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 

of ganglia with their radiating nerves. Two ganglia, just 
above the mouth, one on each side of the gullet, form the 
brain. They are connected by a nerve cord running above 
the gullet. From the brain a nerve cord runs posteriorly 
along each side of the body and joins a pair of visceral 
ganglia just under the posterior adductor muscle. Finally, 
a pair of pedal ganglia is buried in the tissues of the 
foot near its base. Each of these is joined to the brain 
ganglion on the corresponding side by a nerve cord (Fig. 
59). These different pairs of ganglia send nerves to all the 
adjacent parts. 

This system of nerves gives sensation to all parts of the 
body. The senses are not acute, but touch is well developed, 
especially in the point of the foot and margin of the mantle 
and around the edges of the siphons. There is no positive 
evidence that the mussel can taste or smell and it cannot 
hear, but it can feel vibrations through the soil or water. 

Reproduction and life history. — The sexes are separate 
and may sometimes be distinguished by the greater con- 
vexity of the shell of the female. The ovaries and sper- 
maries are similar in appearance and are situated around 
and among the coils of the intestine. The ducts from 
both open on the side of the body near the openings of the 
urinary tubes. The sperms enter the shell of the female in 
the incoming currents of water and fert lize the eggs. The 
eggs then drop into the troughs of the outer gills, which 
serve as brood pouches and retain the eggs until they hatch. 
The embryo mussels are called glochidia and have soft 
bodies inclosed by two triangular valves. Each glochidium 
finally passes out through the exhalent siphon and rests, 
for a time, on the bottom, when it attaches itself to some 
fish by the lower hooklike projections of the valves and 






MUSSELS, CLAMS, OYSTERS, SNAILS, SQUIDS 111 

leads a truly parasitic life for two months, after which it 
undergoes a metamorphosis and falls to the bottom again, 
there to begin an independent existence. 

Distribution and economic importance. — This mollusk 
is widely distributed in the fresh-water streams and lakes 
of the United States. The pearly layers of its shells furnish 
material for large quantities of buttons, and pearls of con- 
siderable value are often found within its shells. Accord- 
ing to recent investigations, it has been shown that pearls, 
at least in the mussel, result from the irritation caused by 
the presence of a minute roundworm parasite in the man- 
tle of this mollusk. The larva of this parasitic worm, es- 
saying to bore through the mantle, rests for a time among 
the loosely connected cells of the latter. As a result, the 
cells of the outer la3^er of the mantle are stimulated to de- 
posit a hard substance, called nacre, around the resting 
larva. This nacre, owing to the fine ridges running across 
it, produces an iridescent object which we call a pearl. 
It is now thought that all pearls are formed in this way, 
although it was formerly held that an undeveloped egg or 
grain of sand lodging between the shell and mantle would 
stimulate the latter to deposit nacre and thus form a pearl. 

The mussel is protected from its chief enemies, the 
raccoon, mink, and otter, by remaining on the bottom 
partly hidden in the mud and by withdrawing into its 
hard calcareous shell. 



^ 



XII. CLAMS, OYSTERS, AND MUSSELS 

Mollusca (continued) 
Class I. — Pelecypoda (hatchet-footed) 

The clams, oysters, and mussels belong to this class. The 
bodies of all are soft and inclosed in a bivalve shell. 

Clams. — Perhaps the two species of clams best known 
because most eaten are the long clam (Mya) and the round 
clam (Venus). The round clam, also known as the "qua- 
hog," "little neck clam," etc., is characteristic of the 
warmer waters. It is common on sandy shores and on 
muddy flats, just beyond the low-water mark, from Cape 
Cod to Texas. It burrows a short distance below the sur- 
face, but is often found plowing at the surface with its shell 
partly exposed. 

On the other hand, the long clam, or soft-shell clam, is an 
inhabitant of cooler waters and extends north to the British 
Provinces, although it overlaps and extends into the terri- 
tory occupied by the round clam. The long clam is re- 
markable for the length of its siphons. These constitute 
the so-called "head," or "neck" and can be extended from 
three to four inches beyond the valves of the shell (Fig. 60). 
When quite young, the long clam begins a barrow in the 
mud and keeps on enlarging and deepening it as it grows 
older, until the clam may finally reach a point eight or ten 
inches below the surface. While lying at the bottom of this 
burrow, the long siphons are extended up to the surface of 

112 



CLAMS, OYSTERS, AND MUSSELS 



113 



the mud within reach of the sea water. In this position a 

stream of sea water carrying food and air goes down one 

tube, is driven through the gills, 

and finally back up the other 

tube to be poured into the sea 

above. 

Oysters. — They are similar in 
structure to a mussel, except 
that they have no foot, or only a 
rudimentary one, and no siphons, 
and the valves of the shell are 
unequal. One valve is hollowed 
out to receive the body of the 
oyster, and the other valve is 
nearly flat. Usually the hollow 
valve is attached to some sub- 
merged object. They live all 
along the Atlantic coast south of 
Cape Cod, and along the Gulf 
coast. Oysters are, probably, 
most extensively grown in the 
Chesapeake Bay. Their eggs, 
which are produced in great 
quantities, soon hatch, and, after 
a few days of a free-swimming 
life, the young oysters attach 
themselves to some objects, usually old shells, and begin 
growing in earnest. It takes an oyster from three to five 
years to become of marketable size. In making artificial 
beds, old shells, pieces of earthenware, and slate are thrown 
into the water for places of attachment for the oysters. 
Oysters live on minute plants and animals found in fresh 

herrick's zool. — 8 




Fig. 60. — Long clam in its 
burrow. 



114 CLAMS, OYSTERS, AND MUSSELS 

sea water. It is necessary that they have plenty of fresh 
sea water and food, and that the mud does not settle over 
them, else they will smother. 

About Ceylon and Australia, in the Persian Gulf, around 
the Philippines, Panama, West Indies, etc., is found the true 
pearl oyster. The American form, which averages about 
nine inches across, is somewhat smaller than the Old World 
form, for the latter often becomes a foot in diameter. Pearl 
fisheries are carried on in many different parts of the 
world, but the most extensive ones are in Ceylon while the 
finest pearls are said to be found in the Persian Gulf. 

The teredo, or ship worm, is a mollusk of strangely 
modified form and interesting and unusual habits. It 
bears very little resemblance to a bivalve mollusk, for its 
body is long and wormlike in appearance, although it has 
a small bivalve shell at one end and two long siphons 
at the other. The embryonic teredo is ciliated and free- 
swimming like the oyster, but instead of settling on some 
object and simply attaching itself, it finds a submerged 
piece of wood, — for instance, the bottom of a ship or piles 
of a wharf, — and begins to burrow into this wood. As it 
grows, it burrows deeper and deeper and lines its burrow 
with a calcareous deposit. When a large number of these 
small mollusks attack the piles of a wharf or the bottom 
of a ship they fairly riddle them with holes a foot or more 
in depth and cause much damage. 

Snails, Slugs, and Seashells 

Class II. — Gasteropoda (stomach- footed) 

To this class belong the snails, slugs, etc. The snails 
have a shell composed of a single piece, while the slugs have 



CLAMS, OYSTERS, AND MUSSELS 



115 




no shell or only a rudimentary one. A head bearing eyes 

and tentacles is present, and the foot forms a large flat 

disk with which the 

animal creeps over 

the ground. 

Snails. — The pond 

snails, Physa and 

Limnsea, are common 

examples of fresh- 
water snails. Their 

habits are much alike. 

Each has a spirally 

coiled shell (Fig. 61) 

and each breathes air FlG - 6i. — Pond snail (Limrum). 

directly, by coming to the surface of the water and taking 

the air in through a tube, the opening of which is just 

within the edge of the 
shell. These snails 
are vegetable feeders, 
living upon bits of 
water plants rasped 
off with a long, flat, 
fleshy band, or rib- 
bon, situated in the 
mouth. This band is 
beset with sharp teeth 
and is known as the 
lingual ribbon. The 
flat, triangular por- 
tion of the body, by 
means of which the 
snails move, is the 




Fig. 62. 



Pond snail (Physa) 
m, mouth. 



a, foot; 



116 CLAMS, OYSTERS, AND MUSSELS 

foot (Fig. 62). The head bears two feelers, or tentacles, 
and a pair of eyes. 

Physa lays its eggs in February or March, in bean-shaped, 
transparent, gelatinous masses, on leaves or sticks in the 
water. Limnsea lays fewer eggs in a mass, and lays them 
later in the spring. 

Besides Limnsea and Physa, the snails that belong to the 
genera Planorbis and Paludina are commonly known as 
"pond snails.' , The members of the former genus have 
shells coiled in a flat spiral, like a roll of tape, and breathe 
air directly, like Limnsea. The members of the latter genus 
have, generally, a longer and more pointed shell and breathe 
by means of gills, much like an oyster. 

Helix. — The common garden snail will serve well as an 
example of the genus Helix (Fig. 63). It has a horn-colored 

shell within which it 
can contract the whole 
body. It has two 
eyes, one at the end 
of each of the large 
tentacles. It breathes 
by means of a lung 

Garden snail. 1 • i , 

which communicates 
with the outside by an opening in the side of the snail's 
neck that can be closed or opened at will. This snail lives 
on plants. In France, some members of the genus, Helix, 
somewhat larger than our own garden snail, are extensively 
eaten as food. 

Slugs. — These are snails that have no visible shell, — 
in fact, some of them have none at all. They usually feed 
only in the night time, hence are not often seen. One, which 
is sometimes found crawling along roads or walks, is known 




CLAMS, OYSTERS, AND MUSSELS 117 

as Limax (Fig. 64). It is dark in color, with two large 
tentacles on its head, and if looked at closely, will be found 
to carry a dark, fleshy cape, the mantle, just back of the 
head. Some slugs leave a white, shining streak wherever 
they go, owing to the fact that they give out a mucus which 
hardens in the air. This is done to make a soft silky path 
over sand and ashes or other harsh substances that would 
irritate the body. They may be traced long distances and up 




Fig. 64. — Slug {Limax) : o, opening to the lung; c, mantle. 

trees, by this shining streak. When ready to descend from 
the trees, some species spin out a thread of the mucus, like 
a spider, and drop down by means of it, instead of retracing 
their path. They often occur in such numbers as to be 
injurious to garden vegetables. 

Sea slugs. — There is a group of marine mollusks, known 
as the nudibranchs, that have no shells in the adult stage, 
hence are often called sea slugs or naked mollusks. The 
gills of these mollusks are usually arranged in tufts that 
project from the sides or back of the animal. The sea slugs 
are of various and striking colors, and vary greatly in shape 



118 CLAMS, OYSTERS, AND MUSSELS 

and size. They are usually found creeping on hydroids or 
upon the seaweeds along the shore. 

Seashells. — The so-called "seashells" are the shells of 
snail-like mollusks that live in the sea. The shells of these 
mollusks are of many different shapes, colors, and sizes. 
The cowries are favorites with collectors. The little oval, 
sharp-spired periwinkles are common along the seacoast. 
Others of these mollusks have very long, slender, many- 
whorled shells. 

Squid, Cuttlefish, and Octopus 
Class III. — Cephalopoda (head-footed) 

As the name indicates, these animals, which include the 
squid, cuttlefish, octopus, etc., have footlike appendages on 
the head. The appendages are really used for grasping, and 
are called tentacles, or arms. Sometimes a shell is present, 
and sometimes it is not. When present, the shell is usually 
internal; but, in the nautilus, the shell is well developed 
and external. 

The squid. — The body of the squid is long and slender 
and incased in a thick, fleshy mantle in lieu of a shell 
(Fig. 65). On each side of the body, at the posterior end, 
is a triangular fin used to guide the body in swimming. The 
head is distinct, bears two prominent eyes and five pairs 
of arms or tentacles, all furnished with cuplike suckers for 
grasping its prey. One pair is usually longer than the 
others, and each member of this pair is expanded near the 
end where it bears four rows of large suckers. The mouth 
is in the center of the cluster of arms at their bases and has 
two strong, horny, black jaws like the beak of a parrot. 
Inside the body is a sac containing black pigment which is 



CLAMS, OYSTERS, AND MUSSELS 



119 



used as a means of defense. When pursued by an enemy, 
the squid ejects some of this pigment which colors the 
water and blinds the 
pursuer. 

The body of the 
giant squid sometimes 
becomes eight or nine 
feet long, while the 
largest pair of arms 
may attain a length 
of twenty or thirty 
feet. 

Cuttlefish.— Thein- 
ternal shell of this 
animal is calcareous 
and furnishes the 
cuttle bone so uni- 
versally used for feed- 
ing canaries. The 
body of a cuttlefish 
is much shorter and 
more oval than the 
squid's. Otherwise 
these two mollusks 
are much alike. It 
is from the cuttlefish, 




Fig. 65.— Squid. 



Sepia, that the pigment is obtained from which sepia ink 
is made. See Figure 66. 

Octopus. — The body of the octopus is more or less egg- 
shaped, and usually not large. A species on the Pacific 
coast is sometimes found with a body one foot long, six 
inches in diameter, and with arms twelve to fourteen feet 



120 



CLAMS, OYSTERS, AND MUSSELS 



in length. The octopus, as its name indicates, has eight 
arms, all of which are provided with suckers. Although 

many thrilling tales 
have been written 
about the devilfish, 
or octopus, not one 
authentic account has 
been given of actual^ 
harm done to man by 
this creature. In fact, 
it seems to be rather 
timid in its natural 
haunts, retreating 
from the presence of 
man. Its food con- 
sists almost entirely 
of crabs, clams, etc. 
The octopus is eaten 
as food by some of 
the people about the 
Mediterranean. 
Pearly nautilus. — This member of the Cephalopoda has 
a well-formed shell coiled in a flat spiral. The interior of 
the shell is divided by partitions into chambers. The ani- . 
mal itself occupies the large outer chamber; and the only 
communication it has with the other chambers is by means 
of a long tube, the siphuncle, which pierces the center of 
each partition and extends through all of them to the tip 
end of the shell. The pearly nautilus is the only surviving 
member of a large group, the ammonites, that lived during 
past ages of the earth's history. The shells of the pearly 
nautilus are common (Fig. 67), but the animals themselves 




Fig. 66.— Cuttlefish. 



CLAMS, OYSTERS AND MUSSELS 



121 



are rare. Oliver Wendell Holmes has made "The Cham- 
bered Nautilus" the subject of one of his finest short poems. 

Characteristics and relationships of the mollusks. — All 
of the members of this branch have soft bodies. With 
the exception of the slugs, squids, cuttlefishes, and a 
few others, their bodies 
are protected by shells 
which are usually com- 
posed of one or two 
valves. The majority of 
mollusks live in water 
and breathe by gills. 
Some breathe air directly 
by means of lungs. 

It is thought that the 
branch Mollusca is more 
closely related to the 
Annulata than to any of 
the preceding branches. 
It is certain that they 
are the highest animals 
so far studied. FlG - 67 - ~ She11 of pearly nautilus - 

Adaptations to environment. — Perhaps the first adapta- 
tion to note is the unique one which enables the long clam 
to live so deep in the mud, out of reach of its enemies above. 
There it lies six or ten inches deep in the mud, and yet, by 
means of its long siphons, is able to get a supply of fresh 
air, water, and food. 

Although the squids, have no outside shell for protection, 
they have a sac full of pigment by which they can color the 
water, blind the pursuer, and so escape. 

The lung of the pond snail, besides acting as a lung, serves 




122 CLAMS, OYSTERS, AND MUSSELS 

also as a means of varying the specific gravity. If a snail 
floating at the surface of the water be touched, the lung 
will force out a bubble of air, thus causing its body to sink 
quickly out of the way of danger. 

The slug has the power to spin a path of silk to protect 
its body from irritating substances. The silk also serves 
as a means of traveling; for example, when the slug is 
descending a tree. 

Economic importance of the Mollusca. — This is probably 
the most important group, economically, that has been 
discussed. The class containing the clams and oysters 
stands first in economic importance. The oyster industry 
is carried on in nearly every seacoast town and village from 
Massachusetts to Texas. The industry reaches its highest 
development in Chesapeake Bay and vicinity. The busi- 
ness gives employment to thousands of persons, and the 
value of the oysters sold amounts to millions of dollars 
annually. 

Mention must be made of the products obtained from 
the pearl oyster. It annually furnishes large quantities of 
valuable pearls, and the mother-of-pearl obtained from 
the shells of this mollusk forms, in the aggregate, a product 
of great value. Buttons, knife handles, penholders, um- 
brella handles, etc., are made from mother-of-pearl. Men- 
tion has already been made of the economic importance 
of the fresh-water mussel. The clams, periwinkles, and 
some snails form a considerable source of food supply. On 
the other hand, the shipworm does great damage by boring 
into piles, wharves, and ships. The slugs often become 
injurious in gardens, but the squid is of value for cod 
bait while the cuttlefish furnishes cuttle bone and the 
material for sepia ink. 



CLAMS, OYSTERS, AND MUSSELS 123 

CLASSIFICATION OF THE EXAMPLES 

Branch X — Mollusca. 
Class — Pelecypoda. 

Order — Pseudo-lamellibranchia. 
Types of Order. 

Ostrea virginiana — Oj^ster. 
Meleagrina margaritifera — Pearl oyster. 
Order — Eulamellibranchia. 
Types of Order. 

Unio complanata — River mussel. 
My a arenaria — Long clam. 
Venus mercenaria — Quahog, or Round clam. 
Class — Gasteropoda. 
Order — Pulmonata. 
Types of Order. 

Physa gyrina — Pond snail. 
Limncea stagnalis opressa — Pond snaih 
Planorbis trivolvis — Pond snail. 
Planorbis antrosus — Pond snail. 
Helix albolabris — Land snail. 
Limax flams — Slug. 
Class — Cephalopoda. 
Order — Decapoda. 
Types of Order. 

Loligo pea! ii — Squid. 
Sepia officinalis — Cuttlefish. 
Order — Octopoda. 
T} r pe of Order. 

Octopus vulgaris — Octopus, 



XIII. CRAYFISH, LOBSTERS, SPIDERS, AND 

INSECTS 

Branch XL — Arthropoda (arthron, joint; pous (pod) foot) 

Like the earthworms and leeches, the members of 
this branch have segmented bodies. In addition to 
this, many of these segments bear appendages of vari- 
ous kinds that, in turn, are segmented; for example, the 
legs of insects. Such appendages mark a decided ad- 
vance over the worms. The branch is at present divided 
into thirteen classes, five of which are discussed here. 
These five classes are represented by the lobsters, 
spiders, millipedes, centipedes, and insects respectively. 

An Example of the Branch — the Crayfish 

The form and divisions of the body. — The crayfish has 
a long, rather thin body, convex above but concave on the 
ventral surface. It is covered, externally, by a hard, cal- 
careous crust that protects the organs and furnishes places 
of attachment for the muscles. The body is divided into 
two regions: the anterior region, or cephalothorax , and the 
posterior region, or abdomen (Fig. 68). The cephalothorax 
is made up of the head and thorax closely joined and is 
covered above and on the sides with a hard, shieldlike 
structure known as the carapace. A transverse groove, the 
cervical suture, on the surface of the carapace, separates the 
head from the thorax. The abdomen is plainly divided 

124 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 125 



into segments similar to the body of an earthworm. The 
cephalothorax is also segmented ; but the segmentation is 
obscured on the dor- 
sal surface by the 
carapace, but shows 
plainly on the ventral 
side. 

The appendages of 
the abdomen. — Each 
segment of the abdo- 
men (in the male), 
except the last, bears 
a pair of appendages 
known as the swim- 
mer ets. These are 
small, segmented, leg- 
like organs held close 
under the abdomen, 
with the exception of 
the last pair. These 
are broad and flat, 
and, together with 




Fig. 68. 



Crayfish. 

the last segment of the abdomen, the telson, form the tail 
fin, or swimming fin. In the female, the first two pairs of 
swimmerets are either very small or altogether lacking. 

Appendages of the cephalothorax. — The appendages of 
the cephalothorax may be divided into five groups: the 
walking legs, five pairs; the foot jaws, or maxillipeds, three 
pairs; the jaws, two pairs of maxilla? and one pair of man- 
dibles ; the antenna?, or feelers, one pair ; and the antennules, 
one pair. 

The walking legs are attached to the thorax and each 



126 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



Heart 



one is composed of several segments which permits freedom 
of movement. Each of the first pair of legs terminates in 
a large pair of forceps, or pincers for grasping. Just an- 
terior to this pair of legs are the three pairs of foot jaws. 
These cover the mouth and aid in crushing the food. The 
next three pairs of appendages constitute the jaws. The 
first pair, the mandibles, are short, hard, and toothed and 
grind the food. The two following pairs are small, soft, 

and weak, but each 
member of the second 
pair carries a curved, 
paddlelike plate, the 
gill scoop, that per- 
forms an important 
function in respiration 
to be explained later. 
On the front of the 
head are the two long 
antennse. Above each 
antenna is a forked 
appendage, the anten- 
nule. 

The situation, form, 
and attachment of the 
gills. — That part of 
the carapace covering 
the thorax is plainly divided into three pieces, a narrow 
middle piece and two wide side pieces that arch downward 
and cover the sides of the thorax. Beneath these two 
large side pieces are two long chambers containing the 
gills. The gills are borne in two sets, an upper set and a 
lower set. The lower set is attached to the basal seg- 




FlG. 



■Cross section of crayfish. 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 127 

merits of the legs and maxillipecls. The upper set is 
attached to the membranes that connect the thoracic 
appendages to the thorax. Each gill is plumelike in form 
with a stem and feathery side branches, and stands 
vertically with the free end pointing upward. In the 
stem are two blood vessels, one for the entrance of the 
blood and one for its exit (Fig. 69). 

The locomotion of the crayfish. — The crayfish has two 
methods of locomotion, walking and swimming. It walks 
with the four posterior pairs of legs, holding the first pair, 
which bears the claws, out in front. The crayfish, at best, 
walks rather clumsily and usually slowly. The water aids 
in buoying up the body, for on land this crustacean walks 
more awkwardly still and the body bumps over the ground 
with evident annoyance. 

In swimming, the broad tail fin is spread out as wide as 
possible and the powerful muscles of the abdomen con- 
tract very quickly and pull the tail with a sudden downward 
and forward stroke beneath the abdomen. This action, of 
course, always forces the crayfish in a backward direction. 
It swims rapidly, and as the animal usually remains close 
to the bottom, the body and dragging legs invariably stir 
up a cloud of sediment that hides the animal from its pur- 
suing enemies. In this backward swimming of the cray- 
fish the unwieldy claws are prevented from retarding the 
rapidity and celerity of its progress by being dragged un- 
resistingly after the body. 

The alimentary canal. — The mouth, which is situated 
in the middle of the ventral surface of the head, opens into 
a short gullet that leads directly upward to a large, capa- 
cious stomach (Fig. 70). The stomach, situated in the 
head, is divided by a constriction in the middle into two 



128 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



portions, a cardiac division and a pyloric division, similar 
to the stomach of a starfish. The pyloric division opens ' 
into the intestine, which runs almost straight to the anal 
aperture on the ventral side of the telson. The pyloric 
division of the stomach is surrounded by two pairs of large 
digestive glands (Fig. 70), often called " livers," that open 



Dorsal bloodvessel Heart 



Ovary 



Brain ganglion 




Greengland 
Mouth 
Digestive gland 
Sivimmereis v ^Ventral bloodvessel 

Fig. 70. — Structure of a crayfish. 

through short ducts into the anterior end of the intestine. 
The stomach is lined by a chitinous layer, and projecting 
from its inside walls are several dark brown, chitinous teeth. 
Strong muscles also run from the outside of the stomach 
to the walls of the body. 

The food and digestive process. — The food of the cray- 
fish consists of both plant and animal matter, preferably 
the latter. These animals sometimes destroy vegetables 
in gardens, but their diet consists chiefly of worms, snails, 
and insect larvae. The crayfish is also a scavenger and 
devours dead fish, clams, and other substances that might 
pollute the water. They sometimes eat their own cast 
skins, the shells of snails, and occasionally, each other. 
Sometimes the food is gnawed off directly by the mandibles, 
and sometimes it is torn off in bits by the large pincers and 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 129 

passed into the mouth by the small pincers on the walking 
legs. 

The food is partly masticated by the mandibles, maxillae, 
and foot jaws. It then passes into the stomach, where it 
is farther comminuted by the churning action of the 
chitinous walls aided by the chitinous teeth. The stomach 
is really a masticating organ and has no digestive function. 

As soon as the food leaves the stomach, it receives the 
fluids from the digestive glands and the work of digestion 
takes place at once in the anterior end of the intestine. 
The food then passes through the walls of the intestine 
directly into the blood which distributes it all over the 
body. 

The circulatory system. — The circulation of the crayfish 
is well developed. The heart (Fig. 70) is situated in the 
dorsal part of the thorax. Five arteries originate from the 
anterior end of the heart. One goes forward to the eyes, 
two (paired) supply the antennae, antennules, and stomach 
with blood, while two (paired) furnish blood to the diges- 
tive glands. From the posterior end of the heart two single 
arteries spring, one of which, the dorsal artery, passes back- 
ward along the dorsal side of the intestine and furnishes 
blood to the intestine and dorsal muscles through many 
branches. The other passes directly downward and joins 
the ventral artery which runs lengthwise of the body below 
the nerve cord (Fig. 70). The ventral artery sends branches 
to the legs and abdominal appendages and muscles. All of 
these arteries divide and subdivide into smaller and smaller 
branches until they end in microscopic vessels called capil- 
laries. The capillaries empty the blood into irregular 
spaces, or sinuses, that occur all through the body between 
the muscles and other organs. These sinuses communicate 
herrick's zool. — 9 



130 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



Nerve ring J 
around guile, " 



either directly or indirectly with one large sinus, or canal, 
that runs along the middle of the thorax and abdomen be- 
low the intestine. From the anterior end of this large 
sinus tubes conduct the blood to the different gills. Here, 
the blood is carried in one tube to the gill filaments, where 
it is aerated and returned through the other gill blood 
vessel to a set of veins, the branchio-cardiac veins, that lead 
to the pericardium, a sac surrounding the heart. Finally 
then, the blood which was sent out from the heart is re- 
turned and poured into a cavity, in the middle of which 
lies the heart. The blood now flows directly into the heart 

through six simple open- 
K$£vetoLtenna, ings in the walls of this 
organ. The holes are all 
provided with valves on 
the inside that prevent the 
return of the blood when 
the heart contracts. There- 
fore, the beating of the 
heart sends the colorless 
blood all over the body 
and brings it back again 
in a continual flow. 

The nervous system. — 
The nervous system is 
tt -71 ""*r^" ~T~ * ■ « u quite similar to that of the 

Jb ig. 71. — JNervous system of a crayfish. ^ 

earthworm (Fig. 71). It 
consists of a brain formed from the fusion of three pairs 
of ganglions and situated in the head anterior to the 
stomach. A double white nerve cord extends from the 
brain along the floor of the thorax and abdomen. As in 
the earthworm, so in the crayfish, the cord passes on the 




; Brain* 
Gullet 



Cephalo- 
thorax 



Ganglion 



Ahdot 



Ganglion 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 131 

right and left sides of the gullet and forms the nerve collar. 
The cords afterward join and become closely fused and 
studded with ganglia in the thorax and abdomen. Many 
of the ganglia have become fused so that there are only 
thirteen distinct ganglia for the twenty body segments. 
From the ganglia nerves pass to all the organs of the body. 

Senses of the crayfish. — The crayfish has the sense of 
sight, touch, smell, and perhaps taste. 

Each of the two large eyes, which are compound, is made 
up of a number of small, square areas, or facets, and is 
borne on the end of a movable stalk. The stalks are ex- 
tensible and can protrude the eyes or withdraw them out 
of the way of danger. In addition, each stalk " is muscular 
and capable of turning the eye, when protruded, to look in 
any direction." 

There are a number of stiff hairs, or seta?, on the external 
branch of each antennule that are supposed to be the seat 
of the sense of smell. 

There is also a sac in the basal segment of each antennule 
that is in free communication with the surrounding water. 
Formerly these were supposed to be organs of hearing but 
are now known to be balancing organs. These aid the 
animal in maintaining its equilibrium. 

The sense of touch is widely distributed over the body,' 
although through such a thick crust it is probably not very 
acute. The antenna?, however, are delicate organs of touch. 

Respiration of the crayfish. — The plumelike gills are 
the organs of respiration. In the filaments of the gills 
the blood is separated from the surrounding water by a 
very thin membrane and the carbon dioxide readily passes 
through this tissue by osmosis and the oxygen is as readily 
absorbed from the water in exchange. The gill scoops. 



132 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 

which were described as paddlelike organs attached to the 
second maxillae, play back and forth in the anterior openings 
of the gill chambers and propel the water forward out of 
the chambers. This causes the fresh water, bearing oxygen, 
to flow into the chambers from below, thus producing con- 
tinuous currents over the gills. 

Method of excretion. — The carbon dioxide, as we have 
just noted, is given up by the blood in the gills. In ad- 
dition, there are two green-colored excretory organs, the 
so-called green glands, situated in the head, just in front 
of the stomach. Each organ consists of a cushion-shaped 
gland and a thin- walled sac, or urinary bladder, that opens to 
the exterior by a duct which has its mouth on the ventral 
side of the basal segment of the antenna. 

Reproduction and life history. — The sexes are separate 
and the abdomen of the female is much broader than that 
of the male. The ovary is situated above the anterior 
end of the intestine and below the heart. The eggs 
are laid the last of March or in April, at least in the central 
states, and are glued by the female to her swimmerets. 
The eggs are small, spherical, and dark colored and adhere 
to the swimmerets in berry like clusters. After some weeks 
the young crayfish issue from the eggs but remain attached 
to the swimmerets for some time. They attain a length 
of about an inch and a half the first season, but during the 
later years grow more slowly and rarely become over five 
or six inches long. 

Regeneration of lost parts. — The large legs of the cray- 
fish are often lost in fighting and sometimes the legs are 
broken off when the body is being pulled out of its old skin. 
In either case, new ones will readily grow out again. When 
a leg is broken off, the blood quickly coagulates at the broken 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 133 

surface, thus stopping more flow and the wound soon 
heals. A crayfish with one claw smaller than the other is 
occasionally found. The smaller claw is simply replacing 
one that has been lost. 

Habitat and habits. — Crayfishes are widely distributed 
over the United States except in parts of New England and 
may be found in most ponds, creeks, rivers, lakes, and in 
many springs. Some species live in holes dug deep enough 
to reach water or, at least, considerable moisture. One of 
these burrows, traced to its bottom in digging a mine shaft, 
extended straight downward for twenty-six feet. 

Some of the burrowing species build mud chimneys about 
the entrances to their burrows. Those that live in water 
usually remain close to the bottom, where they hide during 
the day beneath stones, sticks, or plants. 

Methods of protection. — The crayfish often escapes from 
its pursuer in the cloud of sediment stirred up in its move- 
ments. In addition, the great pairs of claws are very effi- 
cient organs of defense against its lesser enemies, at least. 
Moreover, it lives near the bottom where there are many 
places in which to hide and its threatening attitude, when 
hard pressed, must often frighten its enemies away. Finally , 
the body varies a good deal in color and blends so nicely 
with surrounding objects that it is hard to distinguish. 

Molting of the crayfish. — During the growth of this 
animal it sheds its hard, thick covering from time to time. 
It is evident that the body cannot expand when confined 
in such an unyielding investment, and special provision has 
been made for growth by casting off, or molting the hard, 
limy skin. Before molting, a new soft skin is formed be- 
neath the old one. When ready to molt, the carapace 
splits along the middle line of the dorsal surface, and the 



134 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 

cephalothorax, great claws and all, is drawn out of the old 
skin. Many times a good deal of difficulty is experienced 
in pulling this part of the body from the case and the legs 
are sometimes broken off. Finally, the abdomen is with- 
drawn and the soft, unprotected body is now free from its 
old investment. By the absorption of water, the body soon 
swells to a size much greater than before. This is a critical 
r time for the crayfish, and it hides away in protected nooks 
until the new skin absorbs lime and becomes hard. In the 
process of molting, the lining of the gullet, stomach, and 
intestine is also cast off. 

Economic importance of the crayfish. — Crayfishes are 
used as food to a limited extent in this country and to a 
considerable extent in Europe. They are also of some 
benefit as scavengers. In the southern part of the United 
States they often occur abundantly in cultivated fields 
and cause serious damage to the growing crops. The 
levees of the Mississippi River are sometimes weakened 
by the holes of burrowing crayfishes. 

Crayfish, Lobsters, Shrimps, and Crabs 
Glass, — Crustacea (body inclosed in a crust) 

Lobsters. — What has been said about the crayfish, ex- 
cept with regard to distribution, applies essentially to the 
lobster. Lobsters are found along the Atlantic coast from 
Labrador to Delaware Bay, and from shallow water to a 
depth of one hundred fathoms. They reach their greatest 
size on the rocky shores in the cooler waters from Maine to 
Labrador. They are much prized for food and are caught 
in traps which are baited with fish offal of which the lob- 
sters are very fond. It is now becoming rare to catch a 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 135 



lobster weighing more than five pounds, while formerly 
individuals were common that weighed much more. 

Cyclops. — This crustacean is common in pond water 
aquaria and is large enough to be seen with the naked eye. 
It is free-swimming and, on account of its rapid, jerky 
movements, it is called a water flea. The shape of the 
animal is shown by 
Fig. 72. The single 
eye in the middle of 
the head suggested 
the name "cyclops." 
The antennules, which 
are large, constitute 
the principal organs 
of locomotion. The 
female carries the 
eggs in sacs attached 
to the sides of the 
body. 

Barnacles. — These 
are crustaceans that 
were formerly thought 
to be mollusks. They 
are found in salt 
water, attached to piles, floating timbers, rocks, etc., and 
are one of the prominent causes of foul ship bottoms. 
There are both stalked and sessile barnacles, the former 
being known as "goose" barnacles and the latter as 
"acorn" barnacles. 

The stalk, when present; is a flexible stem, or peduncle 
covered with a finely wrinkled, dark-colored skin. It 
bears the body of the barnacle at its free end (Fig. 73), 




Fig. 72, — Cyclops: e, egg clusters. 



136 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



while the opposite end is firmly attached to some sub- 
merged object. The body of the barnacle is inclosed in a 
sort of bivalved shell which, in reality, is composed of five 
distinct pieces so arranged 
that they form two valves, 
— hence the bivalved ap- 
pearance, by which the barnacles re- 
semble clamlike mollusks. 

The acorn barnacles have no stalk and 
resemble low, blunt pyramids in form. 
They are found attached to rocks and piles 
between tide marks, to ship bottoms, and 
some species, at least, are sometimes found 
attached to the bodies of whales. Some 
species of acorn barnacles grow eight or 
nine inches in length and are sometimes 
eaten for food. 

The life history of barnacles is rather 
complex. The adult lays eggs that hatch 
into queer little animals, each of which is 
called a nauplius, which one would never 
imagine to be connected with an adult 
barnacle. After a time this changes into 
another and different form called the cypris 
form. Finally this, through successive 
changes, develops into the adult barnacle. 
Barnacles are peculiar in having no heart and no distinct 
blood vessels. 

Shrimps. — The shrimps are very closely related to the 
lobsters and crayfish, and are also of considerable impor- 
tance as an article of food. The common shrimp occurs in 
abundance on the eastern coast of North America, from 




Fig. 73.— Stalked 
barnacle. 



•CRAYFISH, LOBSTERS, SPIDERS AND INSECTS 137 



North Carolina to Labrador, and on the western coast of 

Europe. It is between two and three inches long, is usually 

light in color, and is 

found among weeds 

or on sandy bottoms 

in shallow water, but 

may inhabit water to 

the depth of fifty 

fathoms (Fig. 74). 

The southern 
shrimps, or prawns, 
are found in abun- 
dance along the Gulf 
coast and are sent 
to the markets of 
New Orleans, Savan- 
nah, Charleston, New 
York, and Boston. 

Hermit crab. — The 

, , P ., , Fig. 74. — Shrimp. 

abdomen or the her- 
mit crab (Fig. 75) is soft, for the skin is not hardened 
by carbonate of lime; consequently it seeks protection by 

backing into a de- 
serted shell of some 
mollusk of appropri- 
ate size. When the 
shell becomes too 
small by reason of 
the crab's increase in 
size, it is abandoned 
for a larger one. The 

Fig. 75. — Hermit crab. appendages of the 





138 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 




Fig. 76. — Crab, from above. 

or a crayfish very little. The 
covered by the carapace, is very 
length (Fig. 76). The 
abdomen, instead of 
being long and large, 
is short, and is per- 
manently curled be- 
neath the head and 
thorax. In this posi- 
tion it is invisible from 
above (Fig. 77). Both 
pairs of antennae are 
very small. The first 
pair of legs bears 
the great claws for 
grasping. 

The life history of Fig 77 
this crab is rather com- 



abdomen are very 
rudimentary except 
the sixth pair. This 
pair serves to hold 
the body firmly in 
the shell. One of the 
pincers is larger than 
the other and both 
are used to close the 
mouth of the shell to 
keep out intruders. 

Rock crab. — At 

first sight this crab 

resembles a lobster 

cephalothorax, which is 

broad in proportion to its 




Crab, from the under side, 
the abdomen. 



Note 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 139 



plex and interesting. 
From the egg there 
hatches a peculiar form, 
having a long abdomen, 
few or no appendages, 
and large compound 
eyes. This is the larval 
form and is called zoea 
(Fig. 78). After molt- 
ing several times, the 
larva changes to a form 
called megalops (Fig. 79). 
This form somewhat resembles 





Fig. 79. — Megalops of a crab. 



Fig. 78. — Zoea of a crab. 

the adult crab. Finally, 
the form, megalops, 
gradually changes, by 
additional molts, into 
the adult crab. 

The common blue 
crab, found along the 
Atlantic coast from 
Cape Cod south, and 
in the Gulf, is our 
most important edible 
crab. The so-called 
" soft-shelled " crabs 
are simply blue crabs 
that are caught just 
after they have cast 
the old hard skin. The 
body is then soft and 
the flesh is considered 
a great delicacy. 



140 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 

Spider crabs. — The spider crabs are curious-looking 
creatures (Fig. 80) with their small bodies and long, slender, 
fragile-looking legs. For the most part they frequent the 
sea bottom, and their long legs are of great advantage in 
stalking about over the uneven surfaces that they meet in 
such a habitat. Some species permit all sorts of foreign 
bodies, both animals and plants, to become attached to 
their bodies, so that they are effectually concealed, and 




Fig. 80. — Arctic spider crab. 

even when moving, it seems as if a small forest of seaweed 
were being transplanted to another locality. The largest 
crustacean known belongs to the group of spider crabs. It 
is the Macrocheira of Japan. Specimens of this spider 
crab have been caught that measure from twelve to eigh- 
teen feet between the tips of its outstretched claws, while 
their bodies measure only about as many inches in width. 
Fiddler crabs. — The fiddler crabs are abundant along the 
seacoast, especially among salt marshes. They burrow in 
the sand and have the habit of running sideways to and 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 141 

from their burrows. One claw of the male is much larger 
than the other. When these crabs are disturbed, their 
claws are brandished in an amusing manner, strikingly 
suggestive of the motions of a violinist, whence these forms 
have received the common name of fiddler crabs. 

Sow bugs. — These are dark-colored, oval-bodied animals 
with several legs, that live beneath old boards, chunks of 
wood, stones, etc. They are known as sow bugs (Fig. 81), 
and wood lice, and feed largely 
upon vegetable matter, especial- 
ly upon that which is offensive 
to man. Some closely related 
crustaceans, found in the same 
situations as the sow bugs, can 
roll themselves up into a ball, 
and so are called pill bugs. 

Regeneration of lost parts. — 
Like the crayfish, other crus- 
taceans are able to reproduce 

lost parts. A lobster's claw Fig. 81. -Sow bug. Enlarged. 

usually breaks off at a certain point, the "breaking joint," 
and in the course of succeeding molts will be gradually 
reproduced. It is thought by some that this is a means of 
protection, for this breaking adaptation is confined to those 
appendages which are most apt to be seized, namely, the 
five thoracic legs. The antenna? of a lobster will also be 
renewed if broken off. Regeneration takes place in the 
walking legs of shrimps, crayfish, hermit crabs, etc. 

Commensalism. — A certain sea anemone (Adamsia) is 
sometimes found attached to the shell of the hermit crab. 
In this position the sea anemone is carried about, and is 
thus enabled to obtain a more varied and abundant food 




142 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 

supply, while at the same time it affords protection to the 
crab. These animals then are of mutual benefit to each 
other, and the sea anemone is the messmate or commensal 
icon, together; mensa, table) of the crab. Such a rela- 
tion between two animals is called commensalism. 

The same relation exists between the Hyclractinia and the 
hermit crab. Certain species of sponges " are never found 
growing except on the backs or legs of certain crabs." ( 
This is evidently a case of commensalism, for the sponges 
conceal the crabs from their enemies and, in turn, are 
transported to new supplies of food. 

Economic importance of the crustaceans. — Many of the 
crustaceans form an important source of food supply. 
Many millions of lobsters are taken along the Atlantic 
coast annually. The value to the fishermen of the lobsters 
taken off the coasts of the United States is estimated at 
more than one million dollars. The blue-crab fisheries 
yield a product aggregating in value nearly half a million 
dollars each year. Many factories for canning young 
prawns, which are usually sold as shrimps, are located 
along the Gulf coast. The shrimp industry of the Pacific 
coast is very large. 

In a discussion of the economic importance of the 
crustaceans, the smaller forms must be taken into account,, 
for they constitute the principal food of most of our fresh- 
water fishes while young. These minute crustaceans mul- 
tiply very rapidly and become exceedingly abundant. 
Large areas of water, hundreds of miles in extent, in the 
Atlantic Ocean are sometimes colored red by the swarms 
of these minute organisms. At such times fishes congre- 
gate in large numbers to feed upon them, and even whales 
find that these tiny creatures furnish an abundant food 



CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 143 

suppl} r , for their numbers compensate for whatever may 
be lacking in size. 

Chief characteristics of the Crustacea. — They breathe by 
means of gills or through the general surface of the body 
and are therefore essentially aquatic animals. They have 
two pairs of antennae, and in maii}^ the head and thorax 
are combined into a cephalothorax. In some, the body is 
incased in a hard crust formed by the deposition of lime 
carbonate in the skin. 

Some crustaceans are parasitic and fixed, others move 
freely about. Some live along the shore in shallow water, 
while others live in the deep sea. Some inhabit fresh 
water, others prefer salt water, while a few live on land. 



XIV. SCORPIONS, SPIDERS, AND TICKS 



Arthropoda (continued) 

Class. — Arachnida (arachne, spider) 

Although these animals are closely related to the crus- 
taceans, they differ from the latter, in having neither an- 
tennse nor gills. They breathe by means of a system of 
tubes or by lunglike organs, or both. The more familiar 
examples of this class are the spiders, present everywhere, 

the ticks on cattle 
and dogs, and the 
mites on fowls and 
plants. 

Scorpions. — Al- 
though these ani- 
mals are thought to 
be very venomous, 
it is difficult to find 
an authentic case of 
death by a scor- 
pion's sting. The 
larger species in the 
tropics, however, cause serious wounds. The body of the 
scorpion is divided into two distinct regions, the cephalo- 
thorax and the abdomen. The abdomen consists of an 
enlarged portion, next to the thorax, called the preabdomen, 
and a long, slender tail-like portion, the postabdomen (Fig. 
82). The scorpion has one pair of jawlike organs, the 

144 




Fig. 82. — Scorpion. 



SCORPIONS, SPIDERS, AND TICKS 



145 



chelicerce, and two long leglike appendages ending in pin- 
cers resembling those of a crayfish. Scorpions are found 
in the southern states and in tropical countries. They are 
nocturnal in habits, remaining hidden during the day. 

Mites. — Unlike the scorpions, these animals have the 
abdomen joined to the cephalo thorax so closely that the 
body appears as one solid, sacklike piece. The mites are 
small animals and 
many of them are 
parasitic on other ani- 
mals and on plants. 
The so-called red spi- 
der that lives upon 
house plants is a kind 
of mite. The disease 
known as itch is 
caused by a minute 
mite that burrows in 
the skin. A small 
mite, called the chicken mite (Fig. 
in poultry-houses and becomes a serious pest. 

Ticks. — The bodies of ticks are like those of the mites, 
but ticks are usually much larger than mites. One of the 
most important pests, economically speaking, in the 
southern states is the southern cattle tick. It is parasitic 
upon cattle, and is the means of conveying the disease 
known as Texas fever from one animal to another. When 
the female cattle tick gets ready to lay her eggs, she drops 
to the ground from the animal to which she was attached 
and there lays two or three thousand eggs (Fig. 84) . These 
soon hatch into what are known as "seed" ticks, which 
eventually find their way to the bodies of cattle roaming 




Chicken mite. Much enlarged. 

83), occurs at times 



HERRICK'S ZOOL. 



10 



146 



SCORPIONS, SPIDERS, AND TICKS 



in the fields where the "seed" ticks are, fasten themselves 
to their host, and live there until mature. 

The most common tick in the northern states is the clog 
tick. It derives its name from the fact that it is most 
commonly found on dogs, although it often infests other 




Fig. 84. — Southern cattle tick: A, enlarged; B, natural size. 



animals. When fully matured, the female is about one 
half inch long. The back of this tick is marked with bright 
silvery lines and blotches. The young are found on the 
leaves of weeds and bushes, whence they gain access to the 
bodies of passing animals. 

Spiders. — In general, spiders have acquired an unsavory 



SCORPIONS, SPIDERS, AND TICKS 



147 



reputation, but, with few exceptions, they are harmless 
and among the most interesting animals in the world. 
Spiders have four pairs of legs and a pair of jawlike 
appendages, the chelicerce. At the tip of each one of the 
chelicerse is a small hole, the opening of a poison gland 




Fig. 85. — Running spider: P, palpi H, cephalothorax; A, abdomen. 

through which the poison is injected into the prey of the 
spider. They also have attached to the cephalothorax 
a pair of slender, leglike appendages, the pedipalpi (Fig. 
85). The bodies of spiders consist of two parts, the 
cephalothorax and the abdomen. They may have one, 
two, three, or four pairs of single eyes, while certain ones 
living in caves are blind. 



148 



SCORPIONS, SPIDERS, AND TICKS 








//•/, 



Fig. 86. — Spinnerets of a spider. 

each spinneret are many small tubes 
The substance of which the fine 
is a fluid inside the spinnerets; but 
to the air, it hardens and 
forms the thread. In 
wrapping its prey a spider 
spins a band of silk which 
is usually composed of 
very many threads. 

Spiders spin this silk 
for various purposes. 
They make homes of it 
in which to live, sacs of 
it in which to put their 
eggs, traps of it in which 
to catch their prey, and, 
finally, they use it as a 
means of locomotion. ^ 

Suspended from bushes 
and weeds in autumn are 
found egg sacs like the 
one in Fig. 87. It is jug- 
shaped and contains many 



The spinning organs 
(Fig. 86), which are 
near the posterior end 
of the abdomen, on 
the ventral side, con- 
sist of four or six 
finger-shaped projec- 
tions, called spinner- 
ets. On the end of 
called spinning tubes, 
silky thread is made 
the moment it comes 




Fig. 87. — Egg sac of spider. 



SCORPIONS, SPIDERS, AND TICKS 



149 




Fig. 88. — Orb web. Photographed by J. H. Comstock. 



eggs. These hatch early in winter, but no spiders appear 
until the following spring. During the long winter the 
larger and stronger of the young spiders devour the weaker 



150 SCORPIONS, SPIDERS, AND TICKS 

ones so that only the fittest ones survive to become adults 
in the spring. 

Forest paths are often crossed by threads of spider's 
silk. A spider climbs to the end of a branch and spins out 
a thread which is caught by the breeze and waftecl across 
the path, where the end becomes entangled in a branch on 
the opposite tree. 

Certain spiders, known as the ballooning, or flying spiders, 
climb to the end of a post or to the tip of a plant and spin 
silk into the air which is caught and wafted away by the 
breeze. When enough is spun to support the spider, it 
lets go and is borne away by the currents of air. These 
spiders travel long distances in this manner, as shown by 
the fact that they have been seen floating through the air at 
sea far from land. 

The spiders that build the irregular webs, termed cob- 
webs, in dwelling houses belong to the family of cobweb 
weavers. They are small spiders with very slim legs, and 
there are many different species of them. By far the larger 
number live in the fields and spin their webs on bushes. 

Those webs spun by the spiders known as orb weavers 
are marvels of ingenuity and regularity of construction. 
The webs are common on bushes, fences, weeds, etc. (Fig. 
88), but are usually given little attention. The outer frame- 
work of supporting threads is often very irregular; but the 
radiating lines are placed at regular intervals from each 
other, and the spiral is laid on these in a regular manner. 

The radii are dry and inelastic, while the spiral thread 
is sticky and elastic. Some of the orb weavers spin a zig- 
zag band, or ribbon, across the center of the web, evidently 
to strengthen it. Many of the orb weavers are small 
spiders, but some are large. The funnel web weavers spin 



SCORPIONS, SPIDERS, AND TICKS 



151 



their webs upon the grass and the clew often serves to show 
us what an immense number of these webs are spun. 

The trapdoor spiders, found in the southern part of the 
United States and in other warm countries, excavate tun- 
nels in the soil and 
line them with silk. 
Each tunnel is pro- 
vided with a hinged 
lid that fits the open- 
ing very accurately. 

Closely related to 
the trapdoor spiders 
are those very large 
spiders (found in 
the south and south- 
west) known as ta- 
rantulas. They 
live under stones 
and logs, and come 
forth at night. Fig- 
ure 89 shows one 
of these tarantulas 
from western Texas, 
with its egg sac con- 
taining many young 
tarantulas. 

The members of 
at least three different groups of spiders spin no webs at 
all. They catch their prey by running after it or by sud- 
denly jumping upon it. Among these are the common, 
large, rather hairy spiders that are found beneath boards, 
logs, etc., and are known as running spiders (Fig. 85)-; 




Fig 89. — Tarantula and egg sac: A, chelicera 



152 SCORPIONS, SPIDERS, AND TICKS 

the crab spiders, so called because they run sidewise like 
a crab; and the jumping spiders which catch their prey by 
leaping upon it. 

Economic importance of the Arachnida. — The silk of 
spiders has been utilized to some extent in making cloth; 
but it is difficult to wind the silk upon a reel, and it is more 
difficult to rear spiders in sufficient numbers to produce 
silk in paying quantities. Spiders are of some benefit in 
destroying injurious insects. Finally, threads of spider's 
silk are used to form the cross hairs in telescopes and are 
indispensable for this purpose. 

The chicken mite often becomes a serious pest to poultry 
and undoubtedly causes considerable pecuniary loss by a 
decrease in the production of eggs and chickens. The pear- 
leaf blister mite is parasitic upon the leaves of pear trees 
and in some localities inflicts serious injuries on these trees. 
Certain species of mites are often very troublesome to house 
plants, especially in greenhouses. In California, citrus 
trees are subject to the attacks of a species of mite which 
sometimes causes severe losses by weakening the vitality 
of the trees. We have already spoken of the injury caused 
by the southern cattle tick. 

Chief characteristics of the Arachnida. — They have four 
pairs of legs; the head and thorax are combined into a 
cephalo thorax; they have no antennae; the eyes are simple, 
and they do not possess gills but breathe air directly, either 
through a system of tracheal tubes or by means of lung 
sacs. Many of the arachnida are provided with glands 
from which silk is spun. A few, the scorpion, tarantula, 
and one species of spider in the United States, are more or 
less poisonous. With few exceptions, they are carnivorous, 
undoubtedly destroying many noxious insects. 



SCORPIONS, SPIDERS, AND TICKS 



153 



Millipedes 

Class. — Diplopoda (double-footed) 

The millipedes are commonly known as thousand- 
legged worms. The body of a millipede, which is 
usually more or less cylindrical, is divided into many 
ring-like segments and has a distinct head bearing a 
pair of short antennae. Those segments of the body 
that bear legs appear to bear two pairs due to the fact 
that the segments of the body have been closely joined 



c a '" : " * ^bps^^ 



Fig. 90. — Millipede common under decaying logs. 

in pairs. Millipedes frequent damp places and, for the 
most part, feed upon decaying vegetable matter. Occa- 
sionally some species work injury by eating garden 
vegetables. Some of them, when disturbed, emit a 
strong odor from glands opening through pores on the 
segments of the body. The millipedes do not have 
poison glands and are not harmful or dangerous to man. 

Centipedes 

Class. — Chilopoda (lip-footed) 

The centipedes are known as hundred-legged worms. 
They have a flattened body with one pair of legs to a 



154 



SCORPIONS, SPIDERS, AND TICKS 



segment. The head bears a pair of long antennae. The 
first pair of body appendages next to the head are leg- 




Fig. 91. — Centipede from western Texas. 

like in appearance but each one ends in a sharp, piercing- 
claw and has an opening in it through which poison is 
discharged. Centipedes occur all over the United 
States under boards and stones. A species often found 
in dwellings is shown in Figure 92. It has long slender 
antennas and fifteen pairs of legs. It is harmless to 




Fig. 92. — House centipede. 

people and does much good by killing cockroaches and 
other insects. Some of the larger centipedes in tropical 
regions are said to be poisonous. Even the large ones 
in the Southwest can kill mice. 



XV. — INSECTS 

Arthropoda (continued) 
• Class. —Insecta (insects), or Hexapoda (six-footed) 

The number of species of insects is very great and 
exceeds that of any other class in the animal kingdom. 
They are found in every country in the world. Many 
species are very injurious to agricultural and horticul- 
tural interests, while many are very beneficial to the 
farmer and the fruit grower. They are exceedingly 
interesting because of their various and peculiar habits. 
They are convenient to study, because they are easily 
obtained and kept in one's room, where their life history 
and peculiar habits may be observed. 

Example of the Class — the Carolina Grasshopper 

Distribution and habits. — Many writers call all 
grasshoppers, locusts. A locust, more properly, is a 
grasshopper that appears in swarms and migrates over a 
country, devouring the green herbage as it goes. The 
Carolina grasshopper is a large insect from one and one 
half to two inches in length and is common in the United 
States and also in Canada. The male has the interest- 
ing habit of poising in the air a few feet from the ground 
and making a loud, clacking noise, especially during 
the warmer hours of hot summer days. These insects 
(Fig. 93) prefer bare places in fields, or the hot dusty 

155 



156 



INSECTS 



highways, from which they take flight in advance of the 
rider or pedestrian. 




Fig. 93. — Carolina grasshopper. After Lugger. 

Segments and regions of the body. — In studying a 
grasshopper we find that its body, especially its abdo- 

Hindwina Forewing 




Simple 
eye 



Spiracles 



Hind leg 



Middle leg Front leg 



Fig. 94. — Diagram of parts of a grasshopper's body. 

men, is made up of a number of rings, or segments. 
This segmented structure gives flexibility to the body 



INSECTS 



157 




and permits a limited degree of movement. By closer 

study it will be found that there are three distinct 

regions in the body 

of this insect: the 

head, thorax, and 

abdomen (Fig. 94). 

It is well to note, 

just here, that the 

bodies of all insects 

are segmented and 

divided into three 

regions as the body 

of the grasshopper is. 
The head and its 

appendages. — The 

head of this insect 

bears several promi- 
nent appendages ; 

namely, the antennae, or feelers, the eyes, and the mouth 

parts (Fig. 95). The antennae are slender, threadlike 

organs attached to the front of the head near the top. 

Each one is made up of a number of short segments. 

On each side of the 
head, just back of the 
antennae, is a large, 
conspicuous com- 
pound eye. Each 
one is composed of a 
number of regular 
six-sided divisions 
which give it a hon- 

fig. 96. — Portion of grasshopper's eye. eycomb appearance 



Fie;. 95. — Grasshopper's head: a. antennae; c, 
compound eyes; s, simple eyes; u, upper lip. 




158 



INSECTS 



(Fig. 96). In addition to the compound eyes there are 
three simple eyes, one in the middle of the forehead and 
;one at the upper inside corner of each compound eye. 
The mouth parts are fitted for biting and are con- 
structed as follows: on the lower part of the face is a 
notched flap that can be lifted up with a pin (Fig. 95). 
This is the upper lip; just beneath this are two hard, 

black bodies with 
toothed edges, the 
mandibles (Fig. 97). 
Below the mandibles 
is the second pair 
of jaws, the max- 
illae. These are more 
complicated than 
the mandibles and 
each one bears a 
slender prolongation 
like an antenna, 
called a palpus. Finally, below the maxillae is the lower 
lip (Fig. 98), which is notched and bears two palpi. 

The thorax and its appendages. — The thorax of the 
grasshopper is composed of three parts: the prothorax, 
the division next the head; the mesothorax, the middle 
division; and the metathorax, the last division (Fig. 94). 
We can distinguish these divisions by the appendages 
they bear. The first pair of legs is borne by the pro- 
thorax, the second pair by the mesothorax, and the 
third pair by the metathorax. The legs are made up of 
segments with joints, hence are fitted for movement. 
The hind pair is very long, large, and muscular. More- 
over, the thorax bears two pairs of wings that extend 




Fig. 97. — One mandible of a 
grasshopper. 



INSECTS 



159 



backward over the abdomen when the insect is in repose. 
The wings of the first pair are attached to the mesotho- 
rax and are long, narrow, and parchment like, for they 
serve as a protective p 

covering for the hind 
pair. The hind 
wings, which are 
much larger and 
thinner than the 
front ones, are black 
with a broad yellow 
edge. They are at- 
tached to the meta- 
thorax, and when at 
rest, each is folded 
like a fan beneath 
the corresponding 
front wing. 

The abdomen and 
its appendages. — 
The abdomen of the 
grasshopper is the 
largest of the three 
composed of plain, ringlike segments, joined to each 
other by thin, flexible skin, an arrangement that per- 
mits a certain amount of movement of each segment. 
The abdomen bears few appendages, and these are in- 
conspicuous and at the posterior end. In the female 
grasshopper the abdomen ends in four curved, pointed 
pieces which, together, form the ovipositor. It is used 
for making holes in the ground in which to deposit eggs. 
There are also two small, curved appendages, the cerci. 




Fig. 98 



Grasshopper's lower lip: Pa, palpi 

regions of the body. It is 



160 



INSECTS 



Locomotion. — The grasshopper has three ways by 
which it can move from place to place. First, it has 
the two pairs of strong wings suitable for rapid and 
extended flight. Second, it has six well-developed legs 
for crawling, although the first four are used mainly in 
this method of locomotion for the hind ones seem un- 
wieldy and ill adapted to this slow kind of progress. 
Lastly, it uses the large and muscular hind legs for 
jumping. In comparison with its size, the grasshopper 
has extraordinary leaping power. Moreover, each of 
the six legs ends with two hooked claws which enable 
this insect to retain its hold upon objects while crawling. 

The digestive system and food of the grasshopper. — 

The gullet leads upward (Fig. 99) from the mouth, then 

Caeca, 

Urinary tubes 



Intestine 




crtamis Thoracic ganglia Abdominal ganglia 

Fig. 99. — Internal structure of a grasshopper. 

turns posteriorly and quickly widens into the crop. 
The salivary glands lie beneath the crop and connect 
with the mouth through a long, slender tube. The 
stomach succeeds the crop and lies in the abdomen. 
Six pairs of long, tapering pouches, the gastric cceca 
(Fig. 99), surround the anterior end of the stomach. 
They secrete a digestive juice and discharge it into the 
latter organ. A circle of several slender tubes, the 
urinary tubes, arise from the anterior end of the intes- 
tine. They indicate where the stomach ends and the 



INSECTS 



161 



intestine begins. The intestine makes one bend and 
then dilates to form the rectum. 

Grasshoppers eat various kinds of plants, chiefly 
grasses and forage and grain plants. They are voracious 
insects and often eat every growing thing in their path. 

How the insect breathes. — The air enters an insect's 

body through holes along the sides of the abdomen and 

thorax, and passes into tubes known as trachece. This 

is well illustrated by the grasshopper. Figure 94 shows 

one side of a grasshopper with the holes called spiracles, 

Ventral transverse trachea 

Dorsal longitudinal 

trachea 




Lateral longitudinal trachea 
Fig. 100. — Tracheal system of a grasshopper. 

one on each side of the mesothorax and of the first 
eight segments of the abdomen. From each spiracle 
a short trunk runs inward and connects directly 
with two large tubes that run lengthwise, one on each 
side of the body cavity (Fig. 100). Closely connected 
with these are two long tubes running along the 
dorsal side of the body cavity. There are also two 
shorter and smaller air tubes along the ventral side of 
a part of the abdomen. All of these main tracheae 
send off smaller tubes that divide and subdivide into 
smaller and smaller branches which reach every part of 
the body, even entering the legs and wings to some 
extent. 

"The tubes are filled and emptied by a rhythmic, 

herrick's zool. — 11 



162 



INSECTS 



alternately contracting and expanding movement of 
the abdomen called the respiratory movement." 

The circulatory system. — The blood vessels and the 
circulation of the blood in insects are well shown in 
the grasshopper. The circulation of insects is not 
well developed. The only blood vessel in the locust, for 
example, is a long, slender, tubular organ that runs along 
the dorsal side of the body cavity in the abdomen and 
thorax and extends into the head. This is known as the 
dorsal vessel, and that part of it lying in the abdomen is the 
heart, while the anterior part, in the thorax, is the aorta. 

The heart is closed at its posterior 
end, but has openings along each 
side through which the blood enters 
and, by contractions of the heart, 
is forced forward through the aorta 
into the head. Valves within the 
heart prevent the blood from flow- 
ing backward through it. The 
blood is usually a colorless liquid 
and fills all the spaces of the body 
cavity, literally bathing the tissues 
and organs of the insect. It does 
not carry oxygen because this is 
done by the air tubes. Its func- 
tion is to carry the products of di- 
gestion from the alimentary canal. 
fig. 101. -Nervous system The nervous system. —The brain 
of a grasshopper. consists of three large ganglia 

closely connected and lying above the gullet in the head. 
From the brain the nerve cord passes posteriorly, one 
strand going down the left side of the gullet and the other 




Brain gangli 



Thoracic 

ganglia 



] ■Abdominal 

ganglia 



INSECTS 163 

strand down the right side, after which they are united 
again throughout the length of the body (Fig. 101). 
There are three ganglia in the thorax and five in the 
abdomen (Fig. 101). With its eyes the grasshopper 
has a fairly keen sense of sight, for short distances, at 
least. On each side of the first segment of the abdomen 
is a circular tympanic membrane, the ear (Fig. 94). 
The sense of touch is located chiefly in the antennae. 

The excretory system. — The excretory organs of the 
grasshopper consist of the urinary tubes (Fig. 99), 
which lie in a tangled mass about the stomach and 
intestine. They extract from the blood much the 
same products that the kidneys of the vertebrates 
do, and pour them into the intestine to be carried 
out from the body. 

Reproduction. — The ovaries of the female grasshop- 
per lie above the alimentary canal in the abdomen 
(Fig. 99), and, when full of mature eggs, occupy a large 
part of the abdominal space. In the fall, when ready 
to deposit her eggs, the female thrusts the four pointed 
pieces composing the ovipositor into the ground, then 
separates them, thus pressing back the dirt. By re- 
peating this process, she finally forms a hole of the 
required depth to hold her eggs. The eggs are then 
deposited in a capsule or pod where they remain until 
the following spring, when they hatch and the young 
insects appear. The young, the moment they hatch 
from the egg, may be recognized as grasshoppers. They 
are known as nymphs. They eat voraciously and grow 
very fast, becoming mature in about two months. 
During this growth they molt, or shed their skins, 
several times. After the first molt the wings appear 



164 



INSECTS 



as small, backward-projecting pads. With each suc- 
cessive molt the wing pads become larger and larger 
until after the last molt they appear fully developed 
(Fig. 102). Such a development — in which the egg 
hatches into a form resembling the adult — is known as 




Fig. 102. — Nymphs of grasshoppsr: A, first stage; B, second stage; C, third 
stage; D, fourth stage; E, fifth stage; F, final stage. After Emerton. 

a direct development, and insects having a direct devel- 
opment are said to have an incomplete metamorphosis. 
Economic importance of grasshoppers. — Since grass- 
hoppers feed upon grasses, grains, and forage crops, 
they are of considerable economic importance, although 
the Carolina grasshopper does not cause so much injury 
as some other species. The Rocky Mountain locust, 



INSECTS 165 

that in past years has swept over the western states in 
vast swarms, has proven itself one of the worst insect 
scourges that this country has ever seen. At such 
times it literally ate ail the vegetation in its path and 
almost produced a famine in the territory it touched. 
Fifty millions of dollars' worth of farm products were 
eaten by these locusts in the seasons of 1874-1876 
alone. Asia and South America have their swarms of 
migratory locusts. A swarm of locusts covering an 
area of two thousand square miles passed over the Red 
Sea in November of 1889. 

How the grasshopper is protected. — The color of the 
wings blends so nicely with the dusty highways and the 
bare roadsides that many of its enemies must fail to 
find it. Besides, its strong wings enable it to take swift 
flight if in danger. Finally, its strong hind legs enable 
it to leap quickly out of the way of many enemies. 

Another Example of the Insecta — the White 
Cabbage Butterfly (Fig. 103) 

How a butterfly resembles a grasshopper. — The 
butterfly has the body segmented and divided into 
three main regions: head, thorax, and abdomen, similar 
to the grasshopper. It also has six segmented legs and 
two pairs of wings borne by the thorax, as in the grass- 
hopper. Its digestive, excretory, and circulatory sys- 
tems are practically the same as the grasshopper's. 

How a butterfly differs from a grasshopper. — The 
butterfly differs from the grasshopper in the form of its 
wings; the structure of its mouth parts; the kind of 
food eaten and the manner of eating it; in its manner of 



1G6 



INSECTS 



locomotion ; in the structure of the hind pair of legs, at 
least; in its life history; in the form of its antennae; 
and in the absence of simple eyes. 

Wings of the butterfly.— If a butterfly is caught in 
the hand, a fine, dustlike substance is always rubbed 

from the wings by con- 
tact with the fingers. If 
this substance be ex- 
amined under a micro- 
scope, it will be found to 
consist of tiny, flat, 
somewhat fan-shaped 
bodies called scales. The 
wings of butterflies are 
always clothed with 
scales that overlap like 
shingles on a roof (Fig. 
104). They undoubt- 
edly aid in strengthen- 
ing the wing. When 
the scales are all re- 
moved from the wing, 
it appears as a thin 
transparent membrane with veins running lengthwise 
and with few cross veins (Fig. 105). The wings of the 
butterfly are never folded like those of the grasshopper, 
but are held vertically when the insect is at rest. 

The legs of the butterfly. — Although this insect has 
six legs they are weak and are little used for locomotion 
but rather for clinging to objects upon which the 
insect may alight. The hind legs are not muscular like 
those of a grasshopper and are not used for jumping. 




Fig. 103. 



— White cabbage butterfly, 
larva, and pupa. 



INSECTS 



167 



Mouth parts of the 
butterfly. — A but- 
terfly has its mouth 
parts constructed for 
sucking. The man* 
clibles are lacking 
entirely and both 
lips are small and 
inconspicuous. The 
maxillae, however, 
are present, and each 
one is greatly elon- 
gated and grooved 

On its inner Surface. FlG - 104,-Piece of the wing of a butterfly en- 

larged to show the arrangement of the scales. 

Moreover, tney are The scales have been removed from the lower 

ioined together bv * m ^ *° snow * ne pi aces °f attachment. 
their inner surfaces in such a way that the two grooves 
meet and form a tube (Fig. 106) through which liquid 
food is drawn. The proboscis formed by the union of 





Fig. 105. — Wings of a butterfly after the scales have been removed. 



168 



INSECTS 



Maxilla 



Maxilla 




Air tubes 

Fig. 106. — Cross section of the proboscis of a 
butterfly. After Comstock. 



the two maxillae is carried coiled beneath the head 
(Fig. 107). Butterflies live upon the nectar extracted 
from flowers with the proboscis. 

Locomotion of the butterfly. — This insect has two 
methods of locomotion, namely, flying and walking. 

The legs are weak 
and not very effi- 
cient organs for 
walking. At best, 
the walk of a but- 
terfly is jerky and 
feeble. They de- 
pend mainly upon 
their wings for lo- 
comotion, and these 
organs are very efficient. The flight is usually irregu- 
lar, but is swift and capable of long duration. Some 
butterflies migrate regularly according to the seasons. 
The form of the butterfly's antennae. — The antennae 
are composed of short, thick segments and are straight. 
Moreover, they are al- 
ways enlarged at the ends 
with a sort of knob. 

Life history of the but- 
terfly. — In its life history 
the butterfly differs 
markedly from the grass- 
hopper. The former has 
what is known as an in- 
direct development or a 
complete metamorphosis. 
The female lays her eggs on the cabbage leaves and from 




Fig. 107. — Head of a moth, show- 
ing mouth parts modified into a 
long proboscis or sucking tube. 



INSECTS 169 

these there hatch tiny green caterpillars. They eat raven- 
ously, and grow very fast, shedding their hardened skins 
from time to time so that their bodies may stretch and 
become larger. In a few weeks the caterpillars become 
mature. Each one then passes through a great change 
and becomes transformed into 
a quiescent body known as a 
pupa. The pupa is encased Band- 
in a hard, shiny covering and // 

the whole is called a chrysalis. 
The chrysalids of some butter- 

_. J . .... . _ Fig. 108.— Pupa of butterfly. 

mes are beautilully spangled 

with gold and silver spots, but the chrysalis of the cabbage 
butterfly is modest in coloring. It is suspended from the 
cabbage leaf by the tail and by a loose band about the 
middle (Fig. 108). The pupa lies quietly, eats nothing, 
and at the end of about ten or twelve days splits open 
down the back and the adult butterfly crawls out, dries its 
wings in the sun, and in a little while flies away in quest 
of something to eat. 




XVI. OTHER MEMBERS OF THE CLASS— 
INSECTA 

Arthropoda (continued) 

The class Insecta, also called Hexapoda, is divided 
into twenty-five subdivisions or orders. Since many of 
these insects would be quite strange to us, we shall 
confine our attention to seven orders that contain 
the more common and widely known insects. 

Grasshoppers, crickets, cockroaches, etc. — These are 
all closely related insects and belong in the order known 
as Orthoptera (straight wing). The word refers to the 
straight, fanlike plaits into which the hind wings are 
folded when they are at rest. 

The insects in this order have four wings, the front pair 
being thick and not folded, while the hind wings are thin 
and folded in straight, fanlike plaits when at rest. They 
have biting mouth parts and the metamorphosis is in- 
complete. 

There are many species of grasshoppers and they are 
widely distributed over the earth. There are two fam- 
ilies of grasshoppers: the short-horned, those having 
short antennae, and the long-horned, those with long, 
slender antennae. The short-horned family contains 
the true locusts, some species of which are referred to 
in the Bible. Locusts often sweep over a country and 
destroy all herbage. The little red-legged grasshopper 
is common in the northern states, while the large 

170 



OTHER MEMBERS OF THE CLASS— INSECTA 



171 




Fig. 109. — American grasshopper. 



American grasshopper abounds in the southern states 

(Fig. 109). Grasshoppers produce their sounds in 

two different ways. Some species rub the hind legs, 

while at rest, across 

a ridged vein on the 

outer surface of the ^^^gj^^^^^^^^^^^^Rf^v 

first pair of wings, v 

Other species, while 

in flight, rub or 

strike the front edge 

of the hind wings 

against the under surface of the fore wings. This 

produces a loud, sharp, clacking sound. Some species 

lay their eggs in the fall and some in the spring. The 

eggs are laid in a mass of twenty or more, usually in 

the ground but sometimes in logs, stumps, or rails. 

The crickets possess long, slender antennae which are 
unlike the shorter, stouter ones of the common grass- 
hopper. The large veins at the 
bases of the wing covers of the males 
are ridged somewhat like a file (Fig. 
110). When "chirping," or "shrill- 
ing," the cricket elevates the wing 
covers at an angle of about forty- 
five degrees and rubs one against the 
other where the ridged veins are, thus throwing them 
into vibration. Only the male sings. 

The katydids usually possess large green wing covers 
which resemble closely the leaves of trees in which these 
insects live. Katydids, like the crickets, possess long, 
delicate antennae, and the males make their peculiar 
noise in the same manner as the crickets (Fig. 111). 



Fig. 110. — Large vein 
at the base of a crick- 
et's wing. Enlarged 
to show the filelike 
ridges. 



172 OTHER MEMBERS OF THE CLASS — INSECTA 




Fig. 111. — Katydid on an oak leaf. 



The katydids and crickets have ears, or at least hearing 
organs, on their fore legs. 

In kitchens and bathrooms, around water pipes and sinks, 




Fig. 112. — Cockroach: E, egg case. 



OTHER MEMBERS OF THE CLASS — INSECT A 173 



are found those annoying insects known as cockroaches. 
They are often troublesome because they get into places 
where it is not pleasant to us to have them and at the same 
time eat nearly everything they can find. The eggs of a 
cockroach are laid all at a time in a sort of pod or capsule 
(Fig. 112). 

The mantes are common in the South, and are known as 
" praying mantes," or " mule killers." The term " pray- 
ing " comes from the apparently devout attitude assumed 
by the insect. The 
eggs are laid in clus- 
ters on the branches 
of trees or in other 
convenient places. 
The clusters are 
large, usually whitish 
in color, and have 
the appearance of 
being braided on top 
(Fig. 113). The 
mantes are preda- 
cious upon certain 

injurious insects and FlG - 1 13. — Praying mantis, and cluster of eggs. 

for this reason they should be protected. 

Dragon flies. — The dragon flies belong to the order 

Odonata, and are characterized by two pairs of long, netted- 
veined wings and large eyes. The hind wings are as large 
or larger than the front ones; the mouth parts are constructed 
for biting and the metamorphosis is incomplete. 

These are the large graceful insects that are so abundant 
around ponds and along the shores of lakes and streams. 
They are known as " devil's darning needles," " snake 




174 OTHER MEMBERS OF THE CLASS — INSECTA 



doctors/' etc. (Fig. 114). They have long, slender bodies 
and two pairs of strong, transparent wings of about equal 
size and with many longitudinal and cross veins. When 
flying, they dart swiftly back and forth over the water; 
but when they alight, they sit motionless — most spe- 
cies with outspread 
wings — on the dry, 
projecting stems of 
plants. They have 
powerful jaws and 
great round eyes, 
and live upon other 
insects caught while 
on the wing. Most 
of their prey they 
capture and hold 
with their legs and 
eat while flying. 

The eggs of dragon 
flies are either at- 
tached to the stems 
of water plants be- 
low the surface of 
the water or are laid 
loosely in the water, 
or, in some cases, 
are inserted within 




Fig. 114. — Dragon nies. 



the tissues of the plant stems. They hatch into ferocious 
nymphs with strong jaws and enormous appetites. The 
nymphs live upon other aquatic insects, as the larvae of 
mosquitoes, for example, which they devour greedily when 
they are to be found. 



OTHER MEMBERS OF THE CLASS— INSECTA 175 



Squash bug, harlequin bug, chinch bug, et al. — 

The order Hemiptera is a very large one, containing 
besides the bugs named a host of others, as the water 
boatmen, back 
swimmers, stink- 
bugs, and others. 
The mouth parts are 
formed for sucking 
and the metamorpho- 
sis is incomplete. 
Those that possess 
wings have two pairs. 
The basal half of 
each front wing is 
thickened. Most peo- 
ple call nearly any 
insect a "bug", but 
entomologists re- 
strict the term to in- 
sects like those men- 
tioned in this para- 

£Trar)h. In the ^ IG " 115- — Head of a dog-day harvest fly, en- 

t_ £ larged to show mouth parts; Md, mandibles; 

mOUthpartS OI the Mx, maxilla?; S, sheath, formed by the lower 

bugs the mandibles lip ' in wMch the four bristles are carrie(L 
and maxillae have grown out into long, slender, bristle- 
like organs. These four bristles are inclosed in a seg- 
mented sheath formed by the lower lip (Fig. 115). The 
bristles and sheath together form a "beak" or proboscis. 
This beak is plainly seen on the ventral side of the 
thorax, between the bases of the legs of a squash bug, 
harlequin cabbage bug, or bedbug. Many of the bugs 
are injurious to farm crops. They insert their "beaks" 




176 OTHER MEMBERS OF THE CLASS— INSECTA 



into the tissues of the plants and suck out the juices, 
thus weakening, if not killing, the plants. 
The squash bug (Fig. 116) lays its eggs, usually, on 
the under sides of the leaves. 
The young bug passes through 
five stages, gradually getting 
wings and becoming larger, 
before it reaches the adult con- 
dition. 

The harlequin bug, or " calico 
back," or " terrapin bug," as it is 
variously called, is injurious to 
cabbages, turnips, and radishes. 
Its life history is similar to that of 
the squash bug (Fig. 117). There are seven or eight 
generations of the bug during a season in the South. 
Cicadas, scale insects, aphids, et al. — The order 
Homoptera contains many familiar insects like the 
seventeen-year cicada, the scale insects, and the 




Pig. 116. — Squash 
bug. 




Fig. 117. — Life history of a harlequin cabbage bug; e, eggs: n, nymph; 

a, adult. 



OTHER MEMBERS OF THE CLASS— INSECTS 



177 




Fig. 118. — Seventeen-year cicada. 

plant lice, or aphids. Many of these are very injurious. 
The mouth parts are formed for sucking and the meta- 
morphosis is incomplete. Those that possess wings 
usually have four and the front ones are not thickened but 

are thin throughout their 
whole length. 

The seventeen-year 
cicada lives nearly sev- 
enteen years in the 
ground as a nymph on 
the soil humus and sap 
of the roots of trees. 
In the spring of the 
seventeenth year the 
nymphs come out of 
the ground and crawl 
up the trees. The skin 
bursts open on the back, 
the adults (Fig. 118) 
pull themselves out, and 
in a few days lay their 

scale; /, female scale; y, young scale; ~„„„ 4-^ ^\\±~ ™„J *~ 
a, young insect. Enlarged. eggS 111 SlltS made 111 




178 OTHER MEMBERS OF THE CLASS— INSECTA 



the twigs. In the South these cicadas live only 
thirteen years in the earth. The dog-day harvest fly 
goes through its life cycle in two years, but since there 
are two alternate broods the adults appear every year. 
The scale insects are small louselike insects which, in 
many cases but not all, secrete a hard, waxy covering, 

or scale over the body. 
They are often exceedingly 
injurious and of great eco- 
nomic importance. The 
San Jose scale insect is 
probably the most impor- 
tant species in the United 
States (Fig. 119). It is a 
great pest to apple, pear, 
and peach trees. 

The aphids, or plant 
lice, are small, pear-shaped 
insects, some with wings 
and some without, that 
occur on many plants, 
often in enormous numbers. They suck the juices from 
the plants and cause very great harm. The cabbage 
aphid, the green apple aphid (Fig. 120), the cotton 
aphid, and the woolly apple aphid are common forms. 
Butterflies and moths. — The butterflies and moths 
constitute the well-known order Lepidoptera (scale 
wing) . The wings are four in number and clothed with 
fine delicate scales. The metamorphosis is complete, 
the mouth parts are formed for sucking, and the larvae 
are called caterpillars. 




Fig. 120. — Green apple aphid. 



OTHER MEMBERS OF THE CLASS — INSECTA 179 



The butterflies are perhaps better known than the 
moths, because they are more brilliantly colored, as a rule, 
and because they fly in the daytime, while moths for the 
most part fly at night. Moreover, the body of a butterfly 
is slender, while the body of a moth is stouter and more 
robust. The wings of a butterfly, when in repose, are held 




Fig. 121. — Giant swallowtail butterfly. 

vertically, but those of a moth are folded, rooflike, over 
the abdomen. The pupa of a butterfly is naked and is 
known as a chrysalis, but the pupa of a moth is usually 
inclosed in a cocoon of silk, which, in turn, may be wrapped 
with leaves. The wings of both moths and butterflies 
are clothed with scales, and they all have a complete meta- 
morphosis, while the mouth parts of almost all are formed 
for sucking. 



180 OTHER MEMBERS OF THE CLASS— INSECTA 

The swallowtails are our largest butterflies, and are 
easily recognized by the prolonged, tail-like appendages 
of the hind wings. The ground color of the wings is 
usually conspicuously banded and marked with various 
colors of bright or sober hues. The larvae, or caterpillars, 
of these butterflies are common on caraway and 
parsley, and on orange, apple, plum, tulip trees, etc. 
The caterpillars are peculiar and interesting, because 
each one has two fleshy " horns" that may be pushed 
out through a slitlike opening on the top side of the 
front of the thorax. The horns are thought to be for 
the purpose of defense; for in some species, at least, they 
exhale when pushed out a very disagreeable odor. 
There are several species of swallowtails, among which 
are the black swallowtail, the tiger swallowtail, the 
zebra swallowtail, and the giant swallow-tail (Fig. 121). 

The monarch is a very common butterfly and is 
abundant over the middle and eastern United States. 
It has light, tawny brown wings with black veins and 
two rows of white spots around the edges. The cater- 
pillars, which live upon various species of milkweed, 
are yellowish in color and banded with black. The 
chrysalids are bright green, dotted with gold. 

Moths. — Even a beginner will hardly mistake a 
moth for a butterfly. The caterpillars of moths are, as 
a whole, very much more abundant and more injurious 
than those of butterflies. There are also many more 
species of moths than butterflies. The larvae of some 
moths are among our worst insect pests. 

The large green "worms" found on tomato plants are 
the larvae of a magnificent hawk moth (Fig. 122). The 
moth has long, graceful wings that are ash-gray in 



OTHER MEMBERS OF THE CLASS — INSECTA 181 



color, and marked with black or very dark gray, 
abdomen has five yellow spots along each side. 



The 




Fig. 122. 



Tomato moth and tomato worm. 



A small moth, known as the codling moth, lays its tiny 
white eggs on the surfaces of young green apples and leaves 
(Fig. 123). The eggs hatch and the young larvse bore into 
the apple, in most cases entering at the blossom ends, and 
causing wormy apples. 

Sometimes a field of cotton is attacked by caterpillars 
in such numbers that they are known in the South as 
the "army worms." These "worms" are the larvae of the 
cotton moth (Fig. 124). This moth lays its eggs upon the 



182 OTHER MEMBERS OF THE CLASS — INSECT A 

cotton plant, where they hatch into caterpillars that soon 
destroy the leaves if left unmolested. 

One of our larger moths, the polyphemus moth, is shown 
in Figure 125. The larvae of this moth feed upon the leaves 




Fig. 123. — Codling moth, with its egg on the apple at the left and its 
larva in the apple at the right. 

of elm, apple, pecan, etc The peach-tree borer is the larva 
of a clear-winged moth. 

The larvie, or caterpillars, of moths vary greatly in size 
and appearance. Some of them are so small as to be able 
to live all their lives between the upper and under surfaces 
of leaves. Others live in grains of wheat and corn. Some, 



OTHER MEMBERS OF THE CLASS — INSECT A 183 

on the other hand, are five or six inches long and thicker 
than one's thumb. 




Fig. 124. — Stalk of cotton, showing the egg (e), larva (a), pupa (b), and 
adult of the cotton worm moth. 

Flies. — The order, Diptera (two- winged), contains the 
flies, gnats, mosquitoes, midges, and others, and is a very 



184 OTHER MEMBERS OF THE CLASS — INSECT A 



large group. The flies are characterized by having never 
more than two wings. Some possess none. In place of the 




Fig. 125. — Polyphemus moth. 

hind pair borne by bugs, butterflies, and dragon flies, a pair 
of short, knobbed hairs, called balancers, is found. The 

mouth parts are formed 
for sucking and the meta- 
morphosis is complete. 

Though insignificant in 
appearance the mosquito, 
has become one of the 
most important insects 
of this group. It has 
been demonstrated be- 
yond a doubt that a 
certain kind of mosquito, 
called Anopheles, may 

Fig. 126. — Egg rafts of common mosquito l 

(Cuiex). Enlarged. bear within its body, if 




OTHER MEMBERS OF THE CLASS — INSECTA 185 



it has previously bitten a person having malaria, the germ 
that causes malaria. Moreover, whenever this particular 
kind of mosquito bites a person, it injects some of those 
germs into the blood of that individual, thereby inducing 
malaria. Absolute 
proof has also been 
adduced to the effect 
that a certain species 
of mosquito carries 
yellow fever from one 
person to another. 
Thus it has happened 
in recent years that 
the mosquitoes have 
become very notorious 
insects. The female 
of a common species 
of mosquito lays its 
eggs — two or three 
hundred — in small, 
dark, boat-shaped 
masses (Figs. 126 and 
127) on the surface of 
the water. In about 
two days these hatch 
into minute larvre 
called " wiggletails " 
or " wigglers " (Fig. 
128). The " wiggletails " live in the water, but are obliged 
to come to the surface for air. Here they hang head down- 
ward (Culex) with a tube, called the breathing tube, on 
the end of the abdomen, projecting just above the surface. 




B A 

C 

Fig. 127. — Eggs of mosquito, enlarged : 
A, fresh egg with collar; B, egg a little older, 
without collar; C, shell from which the wiggle- 
tail has escaped. 



186 OTHER MEMBERS OF THE CLASS — INSECT A 




Fig. 128. — Wiggler of com- 
mon mosquito, enlarged : r, 
breathing tube. 



ish in color, without feet 
a maggot. When it changes to a 
pupa, it seldom makes a cocoon; 
but many transform within the last 
larval skin which serves as a cocoon. 
Beetles. — This is the largest group 
of insects and forms the order, 
Coleoptera (sheath winged). The 
beetles possess one pair of thin, mem- 



Through this tube, they take in 
the air. They live in this manner 
for about a week and then change 
to pupae (Fig. 129). The pupae 
are also active, and they have the 
anterior end of their bodies greatly 
enlarged. They eat nothing, and 
in a few days their skins split open 
on the back, and the adult mos- 
quitoes (Fig. 130) come forth. 

In general, the mouth parts of 
flies are formed for sucking like 
those of the mosquitoes. Familiar 
members of this group are the 
horsefly (Fig. 131), the blowfly, 
house fly, gnats, midges, etc. 

Flies pass through a complete 
metamorphosis in their life his- 
tory. The 
egg pro- 
duc es a 
larva, usu- 
ally whit- 
It is called 




Fig. 129. — Pupa of com- 
mon mosquito, much 
enlarged. 



OTHER MEMBERS OF THE CLASS — INSECT A 187 



branous wings that are covered, when at rest, by a pair of hard, 

horny wing covers, called the elytra. The metamorphosis is 

complete and the mouth parts are formed for biting. 
The beetles differ from other insects in having this pair 

of hard, horny wing 

covers (Fig. 132). 

They may be told 

almost surely by this 

character alone. The 

front wings of the 

grasshoppers and 

crickets are somewhat 

similar but thinner. 
The Colorado potato dez 

beetle is a familiar ex- 
ample (Fig. 133). It 

is a yellow-lined beetle 

and lays its reddish 

eggs close together in a bunch, usually on the under sides 

of the leaves of potatoes. The soft red larva? soon appear 
and immediately begin to eat the leaves. 
The larva? keep on eating and growing 
for two or three weeks and then go into 
the ground to pupate. 

The May beetles are abundant in 
spring, flying in through the windows 
and bumping about the room. Their 
eggs are laid at the roots of grass, and 

the white grubs live in the soil, eating off the grass roots. 

The larva lives in the ground two or three years and changes 

to a pupa in an earthen cell from which the adult emerges 

in the spring of the year. 




Fig. 130. — Common mosquito, enlarged. 




Fig. 131. — Horsefly. 



188 OTHER MEMBERS OF THE CLASS — INSECTA 



The plum curculio is a small rough beetle with a long 
snout, that lays its eggs beneath the skin of plums, peaches, 
prunes, etc. The larva, or " grub," burrows into the fruit 

and lives there for about 
two weeks, causing 
" wormy" plums and 
peaches. It finally en- 
ters the ground to pu- 
pate, and after about 
four or five weeks the 
adult beetle comes forth. 
The Mexican cotton 
boll weevil is a small 
snout beetle that is ex- 
ceedingly injurious to 
cotton (Fig. 134). It 
came into the United 
States from Mexico and 
is gradually spreading 
over the cotton belt. 
The young larva eats the 
tender inside portions of the squares or bolls and so destroys 
them. 

Other examples of beetles are the carpet beetles, blister 
beetles, ladybird beetles, etc. Many beetles are injurious 
to trees, fruits, grains, and vegetables. 

Bees, wasps, and ants. — These are familiar insects and 
constitute the order, Hymenoptera (Membrane winged). 
They have two pairs of thin membranous wings with few or no 
cross veins. Their mouth parts are formed for biting and 
sucking and the metamorphosis is complete. The bodies of 
the females usually possess a sting, piercer, or saw. 




Fig. 132. — Four common beetles. 



OTHER MEMBERS OF THE CLASS — INSECT A 189 

The hind wings of the bees, wasps, and ants are smaller 
than the front wings, while none of the wings have the 
fine network of veining found in the wings of the dragon 
flies. The larvae of these insects are white, footless grubs. 




Fig. 133.; — Potato stalk, showing life history of the Colorado potato beetle. 



Every one is perfectly familiar with ants ; but not every 
one, perhaps, is familiar with the fact that in a nest, or 
colony, of ants there are always three classes, — males, 
females, and workers. The workers, as their appellation 



190 OTHER MEMBERS OF THE CLASS — INSECT A 

implies, do all the work of the colony, — obtain food, build 
the nest, care for the young and the queen, and fight the 
battles. The queen lays the eggs, but is in no sense the 
ruler. 

There are certain kinds of ants that make slaves of other 
ants. The workers sally forth in a body to war on other 




Fig. 134. — Mexican cotton boll weevil: much enlarged, above; natural 

size, below. 

ants, and, if successful, they bring back larva? and pupae 
and rear them as slaves in their own colony. One species 
of slave-maker ants has become so dependent on its slaves 
that the individuals cannot care for themselves and, if 
left alone, would die. 

On the other hand, some species of ants care very ten- 
derly for certain kinds of insects known as plant lice. The 
plant lice give forth a sweet substance, honey dew, of which 
the ants are fond. The ants of one species actually build 
coverings over the lice to protect them ; while those of 



OTHER MEMBERS OF THE CLASS — INSECT A 191 




Fig. 135. — Nest of Polistes : some of the open cells contain eggs, and some 
larva? ; the closed cells contain pupa?. 

another species take the eggs of the plant lice to their nests 
and care for them during the winter. 

Wasps, hornets, and yellow jackets are mostly social 
insects and live in colonies in 
nests built of papery material. 
They make these nests of bits 
of wood obtained from fences, 
stumps, etc. These bits are 
chewed fine and converted into 
a paste by their jaws, and then 
allowed to dry. 

One kind of wasp builds a Fig. i36.- a wasp (PoZ^ s ) that 

1 # builds an uncovered laver of cells 

nest composed of a horizontal for a nest. 





192 OTHER MEMBERS OF THE CLASS — INSECTA 

comb of many cells, side by side, without any covering (Fig. 

135), and suspended from some object by a small stem 

or peduncle. These wasps are black and ringed with 

yellow or are brownish (Fig. 136). The familiar yellow 
jackets (Fig. 137) and hornets build 
nests composed of several layers of 
comb surrounded by a gray papery 
material (Fig. 138). The nests of 
the yellow jackets are usually built 
in the ground. The colonies of social 
wasps consist of males, females, and 
workers. Every colony is broken up 
in the autumn, only the females sur- 
viving. 

Fig. 137. — Yellow jacket The familiar nests of the mud- 
wasp - dauber wasps (Fig. 139) consist of 

several layers of long cells made of mud, lying side by side. 

They are built in the attics of houses or in barns or other 

outbuildings. The 

adults may be seen 

about puddles of 

water, gathering 

mud to build their 

nests. An egg is laid 

in each cell which is 

then filled with liv- 
ing but paralyzed 

spiders to furnish 

food for the young 

Wasps. FK,138.-NestofVespa. 

Not all wasps are social. Some live alone, hence are 
called solitary. They build their nests in a variety of 




OTHER MEMBERS OF THE CLASS — INSECTA 193 




situations, usually in holes which they excavate in soft 
wood or which they find already made. 

The social bees — honeybees and bumblebees — are of 
considerable economic value to. man. The honeybee 
furnishes us with two most valuable products, honey and 
wax, while the 
bumblebee cross-fer- 
tilizes our fields of 
clover. Yet it is not 
of the social bees 
that we shall speak, 
but rather of the 
solitary ones with 
which we are not so 
familiar. Perhaps 
the small carpenter 
bee, the large car- 
penter bee, and the leaf-cutter bees are the most common 
of the solitary bees. The female of the small carpenter bee 
is about a quarter of an inch long. She selects a twig 
most often of the sumach, that has a soft pith and excavates 
in it a long tunnel. At the bottom she puts in a supply of 
pollen, lays an egg, and then builds a partition above it, f 
lays another egg on pollen, builds another partition, and 
so on, until only room is left for her to rest at the mouth 
of the tunnel, to watch and wait until the young bees appear. 

There is a large carpenter bee that bores into solid wood 
and builds a nest there much like that of the smaller one. 

The leaves of rose bushes are often found with oblong 
and circular notches neatly cut along the edges. This is 
the work of a small leaf-cutter bee (Fig. 140). This bee 
first builds a tunnel in partly decayed wood, then cuts 



Fig. 139. — Xest of mud-dauber : the uncapped 
cells show that the young wasps have become 
mature and flown away. 



HERRICK S ZOOL. 



13 



194 OTHER MEMBERS OF THE CLASS — INSECTA 



oblong pieces from rose leaves and builds a short tube at the 
bottom of the tunnel. The bee then fills the tube partly 
full of a pasty mass of nectar and pollen and lays an egg 
on top. After the egg is laid, the bee cuts circular pieces 

from the rose leaves 
which are a little larger 
than the diameter of the 
tube, and pushes them 
into the mouth of the 
tube, completely stop- 
ping it. In this way the 
tube is filled with short 
cylindrical cells, each 
containing an egg (Fig. 
141). 

Adaptations of insects 
to their environments. 
— Perhaps among no 
other group of animals 
can there be found so 
many and so varied 
adaptations to meet the 

Fig. 140. -Leaf-cutter bee and rose leaf Surrounding conditions 

cut b y it- as among the insects. 

Dragon flies live mainly on mosquitoes, gnats, and other 
small insects caught in the air while on the wing. The 
long, strong wings of the dragon flies and the large eyes 
with which they can see on all sides are distinct adaptations 
for catching these insects. The nymphs of the dragon 
flies live in the water and are furnished with gills to adapt 
them to such a life. 

The bee's hind legs are furnished with thick rows of long 




OTHER MEMBERS OF THE CLASS — INSECTA 195 



rnr- 



■*>• 



■=071 



bristles which serve as receptacles in which the bee carries 
the pollen to the hive. The lower lips of honeybees and of 
bumblebees are long, to enable them to suck nectar from 
flowers. 

The maxilla) of many butterflies and moths have been 
developed into long probosces to enable them to procure 
nectar from deep flowers. This is 
well shown in those large hawk moths 
that frequent honeysuckles at dusk. 

Many grasshoppers are colored like 
the soil on which they live. This is 
well shown in the case of those grass- 
hoppers that are so frequently found 
along dusty highways. It is diffi- 
cult to find one of these insects after 
it alights, so closely does it resemble 
the soil. 

The bodies of fleas are greatly com- 
pressed and these insects are thereby 
enabled " to glide through the nar- 
row spaces between the hairs of their 
hosts." 

The so-called flat bugs have thin flat bodies, which 
enable them to live between the bark and wood of decaying 
stumps and logs. 

Katydids have green wings with veining to resemble 
leaves. The walking sticks greatly resemble sticks. 

A most interesting line of field work may be instituted 
and carried on throughout nearly the whole year, especially 
in the southern states, on the habits of insects and their 
adaptations to their environments. 

Economic importance of insects. — The damage that 



4^ 



Fig. 141. — Nest of leaf- 
cutter bee. 



196 OTHER MEMBERS OF THE CLASS — INSECTA 

insects do to agricultural and horticultural interests is apt 
to overshadow the benefits these small animals confer upon 
mankind. We should not forget that bees are specially 
useful in cross-fertilizing many of our fruits and certain of 
our forage plants, notably red clover. The usefulness of 
the bumblebee, in this respect, was demonstrated when it 
was found that red clover in Australia did not produce seed 
until this bee had been imported to cross-fertilize the 
flowers of the clover plant. 

A most notable demonstration of the value of insects in 
the cross fertilization of fruits has been made by the Bureau 
of Entomology of the United States Department of Agri- 
culture in connection with fig growing in California. To 
produce the best quality of fruit the flowers of the culti- 
vated fig must be cross-fertilized with the pollen from the 
wild fig. The structure of the fig flower is such that this 
can be done only by a tiny insect, the Blastophaga, formerly 
not found in the United States. After many trials and 
most praiseworthy persistence the Bureau of Entomology 
succeeded in importing this insect from the fig-growing dis- 
tricts of Europe and in establishing it in California with the 
result that that state is now producing, annually, many 
tons of figs pronounced by experts to be superior, in some 
respects, to the imported Smyrna figs. 

Scale insects give us cochineal and carmine and some of 
them produce the shellac used in finishing furniture, etc. 
The products of the honeybee amount to hundreds of 
thousands of dollars each year. 

After all, it is in the role of destroyers of fruits, garden 
crops, forest trees, and cereals that insects assume their 
greatest economic importance. It is estimated that the 
chinch bug destroys forty million dollars' worth of wheat 



OTHER MEMBERS OF THE CLASS — INSECTA 197 

every year. The Mexican cotton boll weevil destroyed 
between ten and fifteen millions of dollars' worth of cotton 
in Texas in 1903. The weevils and the angoumois grain 
moth that live in stored grains destroy many million bushels 
of corn, wheat, peas, and beans every year. Professor 
Sanderson says that three hundred million dollars is a con- 
servative estimate of the amount of damage done annually 
by the Colorado potato beetle, tobacco worm, cotton worm, 
boll worm, plum curculio, San Jose scale, cabbage worms, 
chinch bugs, grain weevils, and other insects. 

Chief characteristics of the insects. — Insects have six 
legs; breathe air directly through a system of tracheal 
tubes ; pass through certain remarkable changes, or meta- 
morphoses, in their life history ; possess one pair of antennae, 
two compound eyes and, in many cases, one or more simple 
eyes, and usually wings in the adult stage. 



CLASSIFICATION OF THE EXAMPLES 

Branch XI — Arthropoda. 
Class — Crustacea. 

Subclass — Entomostraca. 
Order — Cirripedia. 
Types of Order. 

Lepas anatifera — Barnacle. 
Balanus balanoides — Acorn shell. 
Order — Ostracoda. 
Type of Order. 

Cypris virens — Water flea. 
Order — Copepoda. 
Type of Order. 

Cyclops serrulatus — Water flea. 
Subclass — Malacostraca. 
Order — Decapoda. 



198 OTHER MEMBERS OF THE CLASS— INSECTA 

Types of Order. 

Homarus americanus — Lobster. 
Cambarus affinis — Crayfish. 
Crangon vulgaris — Shrimp. 
Eupagurus longicarpus — Hermit crab. 
Cancer irroratus — Crab. 
Chioncecetes opilio — Arctic spider crab. 
Gelasimus minax — Fiddler crab. 
Order — Arthrostraca. 
Type of Order. 

Oniscus asellus — Sow bug. 
Class — Arachnida. 

Order — Scorpionida. 
Type of Order. 

Buthus carolinus — Scorpion. 
Order — Araneida. 
Types of Order. 

Aranea frondosa — Orb -web spider. 
Bothriocyrtum calif ornicwn — Trapdoor spider. 
Eurypelma hentzii — Tarantula. 
Order — Acarina. 
Types of Order. 

Boophilus annulatus — Cattle tick. 
Tetranychus telarius — Red spider. 
Dermacentor americanus — Dog tick. 
Class — Diplopoda. 

Type of Class. 

Julus nemorensis — Millipede. 
Class — Chilopoda. 

Types of Class. 

Scutigera forceps — House centipede. 
Scolopendra morsitans — Centipede. 
Class — Insecta. 

Order — Orthoptera. 
Types of Order. 

Dissosteira Carolina — Carolina grasshopper. 
Gryllus abbreviatus — Cricket. 
Microcentrum retinervis — Katydid. 



OTHER MEMBERS OF THE CLASS— INSECTA 199 

Order — Odonata. 
Type of Order. 

Anax Junius — Dragon fly. 
Order — Hemiptera. 
Types of Order. 

Anasa tristis — Squash bug. 
Notonecta undulata — Back swimmer. 
Euschistus servus — Stinkbug. 
Cicada tibicen — Dog-day harvest fly. 
Cicada septendecim — 17-year cicada. 
Order — Lepidoptera. 
Types of Order. 

Papilio cresphontes — A swallowtail. 
Alabama argillacea — Cotton worm. 
Carpocapsa pomonella — Codling moth. 
Order — Diptera. 
Types of Order. 

Culex pipiens — Mosquito. 
Musca domestica — House fly. 
Calliphora vomitoria — Blowfly. 
Tabanus atratus — Horsefly. 
Order — Coleoptera. 
Types of Order. 

Leptinotarsa dccem-lincata — Colorado po- 
tato beetle. 
Lachnosterna fusca — May beetle. 
Adalia bipunctata — Ladybird beetle. 
Anthonomus grandis — Mexican cotton 
boll weevil. 
Order — Hymenoptera 
Types of Order. 

Monomorium pharaonis — Red ant. 
Formica difficilis — Slavemaker ant. 
Vespa germanica — Yellowjackets. 
Eumenes fraternus — Mason wasp. 
A pis mellifica — Honeybee. 
Ceratina dupla — Small carpenter bee. 
Megachile mendica — Leaf-cutter bee. 



XVII. BRANCH XII. — CHORDATA {chord, cord) 

If we recall, thoughtfully, all the animals thus far studied, 
we shall find that they are conspicuous for the lack of one 
thing. That is, that they have no backbone or anything to 
take the place of a backbone; hence they are called inverte- 
brates {in, without; vertebra, joint). All the remaining 
members of the animal kingdom are conspicuous from the 
fact that they have a spinal column or some structure that 
takes the place of it at some period of their life. Those 
that possess a real backbone, as most fishes, all birds, and 
mammals, are known as vertebrates. Some of the animals 
with which we are yet to become acquainted have no 
spinal column, but they do have a structure that takes 
the place of it. This is a soft, flexible rod, or cord, that 
tapers to both ends and lies along the back, where the 
backbone lies in vertebrates. Again, a very few animals 
— some sea squirts — possess this cord only in their youngest 
stages, losing it entirely when full grown. Finally, all 
vertebrates, as fish, birds, and mammals, possess this cord 
in their embryonic stages, but its place, in most, is taken 
later by a spinal column. Hence all animals, not included 
in the eleven branches already discussed, possess, either in 
their youngest stages or throughout life, a soft, flexible 
cord, or rod, known as a notochord, and consequently they 
are grouped together in one branch called the Chordata. 

Moreover, when any animal so far noted has had a cavity 
in the body, it has had but one; for example, the hydra, 

200 



CHORDATA 201 

sea anemone, earthworm, and squid. In the hydra this 
cavity serves as a digestive tract. In the earthworm the 
cavity, or ccelome, as it is properly called, contains blood 
vessels, nerve cords and ganglia, and an alimentary canal 
(Fig. 142, /). Then we may say, in general, that inverte- 
brates have one cavity in the body. On the other hand, in 
most of the members _^^ 

of the Chorda ta, and * fV^ 

especially in the ver- f^ Ql^^... h n—jJ&£~^^L 
tebrates, we find two f ^^ \ f ^^ \ 

cavities in the body I f -J 1- « -I -f--- J 1 

(Fig. 142,7). One of V ^^ J Y ^^ J 
these cavities contains ^ ^^^•-n. &— -% ^--Q ^^ 
the blood vascular / v 

System, a Series Of Fig. 142. — Diagrammatic cross sections of the 

nerve ganglia and b ° dy ofan invertebrate (/), and a vertebrate 

° ° ' (V). Note the one body cavity in 7, and the 

tne alimentary Canal. two body cavities in V : a, alimentary canal; 

This CavitV COrre- *>' blood vascular system ; n, nervous system ; 

. . . c, spinal cord. 

sponds quite closely 

to the one cavity found in the bodies of the inverte- 
brates. The other cavity in the Chordata contains the 
brain and spinal cord, and we find nothing among the in- 
vertebrates to correspond with this cavity. It is well to 
bear in mind that the possession, by the Chordata, of a 
second cavity containing the brain and spinal cord consti- 
tutes a well-marked difference between this branch and 
all the invertebrates. 

Note that the two cavities in the Chordata are separated 
either by a notochord or by a series of bony segments that 
make up the spinal column. Note also that in whatever 
animal a spinal column is found it is always preceded by a 
notochord in the embryonic stages of that animal. With 



202 CHOKDATA 

these differences in mind we shall briefly discuss one class 
of the Chordata and then pass to the better-known verte- 
brates. 

CLASSIFICATION OF THE CHORDATA 

Branch XII — Chordata. 

Sub-branch — Urochorda. 

Class — Urochorda or Tunicata. 
Order — Ascidiacea. 
Type of Order. 

Ascidia species — Sea squirt. 
Sub-branch — Vertebrata. 
Division A — Acrania. 
Class — Acrania.. 
Type of Class. 

Amphioxus lanceolatus — Lancelet. 
Division B — Craniata. 

Class I — Cyclostomata. 
Type of Class, 

Petromyzon marinus — Lamprey. 
Class II — Pisces. 
Type of Class. 

Perca flavescens — Perch. 
Class III — Amphibia. 
Type of Class. 

Bufo lentiginosus — Toad. 
Class IV — Reptilia. 
Type of Class. 

Crotalus horridus — Rattlesnake. 
Class V — Aves. 
Type of Class. 

Passer domesticus — Sparrow. 
Class VI — Mammalia. 
Type of Class. 

Lepus sylvaticvis — Rabbit. 



XVIII. UROCHORDA AND VERTEBRATA 



Branch XII. — Chord ata {continued) 

Class — UROCHORDA (with notochord) 

Sea Squirts 

Sea squirts. — The animals of this class are not well 
known to most of us. They are called ascidians as well 
as tunicates. They are marine animals, some species 
of which live a free-swimming life, while others are attached 
to rocks and are unable to 
move from place to place 
any more than the sponges. 
Like the sponges, many of 
them reproduce by bud- 
ding, thus forming large 
colonies of individuals. 
Other species pass a soli- 
tary existence. 

In general, their bodies 
are barrel-shaped (Fig. 143), 
and covered with a flexible, 
leathery mantle or tunic, 
composed of two layers, the 
inner one of which usually 
contains many longitudinal 
and transverse muscles. In 
most species there are two 




Fig. 143. 
203 



ttea squirt or ascidian. 



204 UROCHORDA AND VERTEBRATA 

apertures to the body, one for the ingress and the other for 
the egress of water. From the latter opening the water is 
forced in a stream by the contraction of the muscular mantle. 
This habit gives them the common name, sea squirts. 

Most of the ascidians possess a notochord only in the 
larval stage, losing it entirely as they become adults. 

VERTEBRATA 

Fishes, frogs, reptiles, birds, and mammals. — By far the 

greater number of animals belonging to the branch Chor- 
data possess a spinal column, or backbone made up of 
bony segments called vertebrae, — hence the name verte- 
brates. The animals named at the beginning of this 
paragraph are familiar examples of vertebrates. The body 
of a vertebrate is divided into three regions : head, trunk, 
and tail. When limbs are present, there are never more than 
two pairs. In general, vertebrates have an internal skele- 
ton. Some have also a partial external skeleton, as croco- 
diles, tortoises, and others, while many possess vestiges of an 
external skeleton represented by nails, horns, hair, feathers, 
hoofs, etc. Among vertebrates we find two kinds of respi- 
ratory organs, namely, lungs and gills. The land-living 
vertebrates and many of those living in the water are fur- 
nished with lungs, but the fishes and a few of the amphibians 
possess gills for breathing. In all except the lancelet 
there is a single contractile cavity, or heart. In all there 
is a system of blood vessels for the circulation of the blood. 

Lancelet 

Class. — Acrania 

Lancelet. — The lancelet is the lowest vertebrate. It 
lives the life of a fish and somewhat resembles a fish in form, 



UROCHORDA AND VERTEBRATA 205 

but has no distinct head, no brain, and no eyes, legs, or fins. 
It is about two inches long and is found buried in the sand, 
along the shores of the Mediterranean Sea, North Sea, Eng- 
lish Channel, our Atlantic and Gulf coasts, West Indies, coast 
of California, etc. It is transparent, flattened from right 
to left, and pointed at either end, hence its resemblance to 
the head of a lance. 

The mouth is simply a slit surrounded by slender fila- 
ments, called cirri. The blood, which is colorless, is puri- 
fied by internal gills. No true heart is present. The 
lancelet has no backbone, but the notochord persists 
throughout life, and, just above it, lies the spinal cord. 



Fig. 144. — Diagram of a lancelet; m, mouth; gs, gill slits; s, spinal cord; 
n, notochord ; i, intestine ; tf, tail fin. 



The lancelet shows its relationship to the vertebrates by 
the possession of the notochord, spinal cord, and gill 
slits in the walls of the pharynx. 

Lampreys 

Class. — Cyclostomata 

Lampreys. — They are long, smooth, and cylindrical, ap- 
pearing much like eels. In fact, they are often called " lam- 
prey eels." There are at least twelve species in the United 
States. They vary in length from one to two feet. The 
mouth is circular and is formed for suction. The interior 



206 UROCHORDA AND VERTEBRATA 

surface of the mouth of the common sea lamprey is covered 
with strong teeth and even the tongue is furnished with 
three large teeth. By means of the suckerlike mouth the 
sea lampreys attach themselves to the bodies of fish and, 
with the strong teeth, rasp off bits of flesh, at the same 
time sucking the blood. 

Just back of the mouth, on each side of the neck, is a 
row of seven round holes (Fig. 145). These open into short 
tubes that lead to sacs in which the gills are situated. Con- 




Fig. 145. — Sea lamprey. 

sequently, in spite of the fact that the mouth of the lam- 
prey is closed, the gills are bathed by fresh sea water that en- 
ters through the circular holes along the sides of the neck. 
They have no backbone, but the notochord persists through 
life. Attached to the sides of the notochord are small 
cartilaginous projections that suggest vertebrae. 

Lampreys have a rudimentary brain, a spinal cord, and 
two eyes that are without eyelids but are covered by a 
thin transparent skin. The sea lampreys go up rivers in 
the spring, build rude nests out of small stones, and lay 
their eggs there. In the autumn the young return to the 
sea. The fresh- water lampreys in Cayuga Lake, N.Y., go 
up the small streams to lay their eggs. 

The hagfishes which belong to this class and greatly re- 



UROCHORDA AND VERTEBRATA 207 

semble the lampreys are marine and are parasitic. They 
attach themselves to the bodies of fish and actually bore 
through the body walls and enter the abdominal cavities 
of their hosts. These and the lampreys are the only 
parasitic vertebrates. 



XIX. FISHES 

Branch XII. — Chord at a {continued) 

Class. — Pisces 

The fishes constitute the largest class of the vertebrates. 
They vary greatly in shape, size, and general appearance 
and are found everywhere over the earth. Three thousand 
species are now known to occur in North America alone. 

An Example of the Class — the Perch 

General form. — The body of the perch is long, deep, and 
thin from side to side and has a wedge-shaped head and a 
somewhat rounded tail ending in a fin, the principal organ 
of locomotion. There is no neck for the head is joined 
directly to the trunk. Therefore, the body is divided into 
three regions : head, trunk, and tail — the latter comprising 
that portion of the body beyond the anal opening. 

Scales. — The body, except a part of the head and the 
fins, is covered with small scales that overlap each other 
like shingles and constitute the exoskeleton. The scales 
are horny outgrowths of the true inner skin, and they are 
covered with a thin, slimy membrane, the epidermis. The 
free, posterior edge of a scale is rounded, while the anterior 
edge, by which the scale is attached, is scalloped like the 
shell of certain mollusks. 

Eyes. — There are two large eyes, one on each side of the 
head. They have no eyelids, but a thin, transparent skin 

208 



FISHES 209 

passes over the outside layer, or cornea of each eye. The 
pupil is large and conspicuous,. and each eye is surrounded 
by a circular fold of skin and set in a protective socket. 

Mouth and nostrils. — The perch can open the upper 
and lower jaws so wide that the mouth appears as a circular 
aperture almost as large as the circumference of the body. 
The perch lives upon smaller fish, worms, insects, etc., 
which are caught alive in its capacious mouth. The mouth 
is furnished with numerous small teeth that are present, 

Dorsal Jins 

JCaudal 
(§)0»m^to/* ^--— -SJ^jg fin 

lAnalfln 
'Pelvicfhi 

Fig. 146. — Diagram of a perch. 

not only on both jaws, but on the roof of the mouth and roof 
and floor of the pharynx. The teeth are not strong enough 
to masticate the food to any extent, but are suited to hold 
the prey of the perch. 

In front of each eye, on the head, are two openings, the 
nasal apertures, or nostrils. These do not communicate 
with the mouth as in the mammals, but lead to a pair of 
sacs, the nasal sacs, situated within the head above the roof 
of the mouth. 

Fins. — The perch has eight fins of which four are borne 
in pairs, therefore known as the paired fins. The remaining 

herrick's zool. — 14 



210 FISHES 

four are borne singly in the middle plane of the body and 
are therefore called median fins. The first pair of fins is 
borne, one on each side of the body, just back of the gill 
openings. These are the pectoral fins and correspond to 
the fore limbs of a mammal. The second pair, the pelvic 
fins, is placed a short distance behind the pectoral fins and 
on the ventral side of the body. These are homologous to 
the hind limbs of a mammal. There are two dorsal fins 
borne in a middle line on the back, one just behind the other. 
There is also a single fin, the anal fm, borne on the ventral 
side of the body in front of the tail fin. Finally, the tail 
terminates in a single wide fin, the caudal fin (Fig. 146). 

A fin is simply an expanded fold of the skin with a sup- 
porting framework of spines, or rays. Some of the rays 
are segmented and are known as soft rays while others are 
stiff, unsegmented spines. 

The gills. — On each side of the perch's head is a flaplike 
organ, the gill cover, or operculum. The posterior margin 




Fig. 147. — Head of fish, with gill cover cut away to show gills. 

of each gill cover is free and in a living fish, a stream of 
water is constantly flowing out through the opening between 
the gill cover and the body. Beneath each gill cover are 
four red comblike gills. Each gill consists of a double row 



FISHES 



211 



of fleshy filaments attached to the posterior and outer border 
of a slender bony arch. On the front and inner side of each 
arch is a row of teethlike projections, the gill rakers. Be- 
tween the gills are long, slitlike openings, or clefts (Fig. 147). 

The blood enters each gill from the lower end, passes 
out into the filaments, and returns to leave the gill through 
an artery from the upper end. Thus there is a constant 
flow of blood through each gill. 

Manner of breathing. — Under natural conditions the 
perch's mouth and the gill covers are seen to open and close 



3rain 



Spinal cord 




Bach bone 

^ uth <8&<£t^^ bladder 

"~ -— — <^^T^r> c^s^ooo^mmTr^y^ r ^\vurinary maimer 

Heart 

Gallbladder Spleen 

Fig. 148. — Internal structure of a fish. 

alternately. During this action water is taken into the 
mouth, forced through the gill clefts and over the double 
rows of filaments, and thence out through the gill openings. 
Thus the gills are being constantly bathed with fresh water 
laden with oxygen. The current of blood through the fila- 
ments is separated from the water by a very thin, delicate 
membrane through which an exchange of oxygen and car- 
bon dioxide readily takes place. The process is similar to 
that already described in the crayfish and mussel. 

Alimentary canal. — The mouth and pharynx constitute 
a single large space that leads to the short, wide gullet. 



212 



FISHES 



The gullet opens into the stomach, which consists of an 
anterior region that extends straight back and ends blindly; 
a posterior region that leaves the anterior region at right 
angles near its middle; and three long, cylindrical, blind 
sacs, the caeca (Fig. 148). The intestine begins just back 
of the caeca and after one or two turns terminates at the 
anal opening. The liver lies in the anterior end of the body 
cavity and has on its posterior surface a gall bladder which 
empties its bile through a short duct into the anterior part 
of the intestine. 

Circulatory system. — The heart of the perch lies between 
the gills and is in close relation to them. It is inclosed in 



Efferent gill arteries I fepatic arte ry 

Caudalvein- 




heart 



Kidney 

~ 'Ovary 
_^^i^X^Almienta,ry canal 
Hepeticvem %,iver Mesenteric artery 

Fig. 149. — Circulation of a fish. 



the pericardial cavity which is entirely separate from the 
main body cavity. The heart consists of three parts, the 
sinus venosus, the thin-walled auricle, and the muscular 
ventricle, placed in the order named, beginning at the 
posterior end. The ventricle pumps the blood from its 
anterior end through a large artery that sends a branch to 
the lower end of each gill. The blood then flows upward 
through the gill filaments and leaves them from the dorsal 
ends through arteries that finally meet in the median plane 
on the dorsal side of the body cavity and form the dorsal 



FISHES 213 

artery, which, in turn, sends off branches that supply the 
different organs of the body. These branch arteries finally 
form minute capillaries that permeate all the tissues. The 
capillaries unite to form veins through which the blood is 
conveyed to the sinus venosus and from this into the thin- 
walled auricle and then into the ventricle, thus completing 
the circuit (Fig. 149). 

Brain and spinal cord. — Looking at the brain from the 
dorsal side it is seen to consist of several divisions. The 
two hemispheres in front constitute the cerebrum. The 
olfactory lobes project from the anterior ends of the cere- 
brum and send the olfactory nerves forward to the nasal 
cavities. Posterior to the cerebrum are the two large 
optic lobes, the widest part of the brain. Behind these is 
the cerebellum, a single, undivided portion. Underneath 
and posterior to the cerebellum is the medulla oblcngata, the 
enlarged end of the spinal cord which extends posteriorly 
through the bony tube formed by the dorsal projections of 
the vertebra?. 

Plan of structure. — The fish presents an entirely new 
plan of structure. The nervous system is on the dorsal 
side of the body, while the nervous system of the inverte- 
brate animals, for example, the earthworm, is on the ventral 
side of the body. Moreover, the main nervous system of 
the perch is inclosed in a long cavity on the dorsal side of 
the body. Below this cavity and separated from it is the 
large body cavity containing the alimentary canal. There- 
fore, in a cross section of the perch, two cavities appear, 
while in the cross section of the body of an earthworm only 
one cavity appears. As we pointed out earlier, these dis- 
tinctions are characteristic of vertebrates and invertebrates. 

How a fish swims. — In the dorsal part of the abdominal 



214 



FISHES 



cavity of the perch there is a long, thin-walled sac, the air 
bladder. It is filled with air and is evidently an organ for 
regulating the position of the fish in the water. The gas in 
the sac is compressed by the contractions of its muscular 
walls and the fish sinks. Vice versa, when the gas expands, 
the bladder becomes larger, the body lighter, and it rises. 
In some fishes that rest most of the time 
on the bottom there is no air bladder. 
In other fishes it serves as a lung. 

The posterior part of a fish is flexible 
and has a consequent freedom of motion 
not found in the more rigid anterior 
part. The tail and tail fin constitute 
the principal organ of locomotion. A 
quick siclewise stroke with the tail in one 
direction followed instantly by another 
stroke in the opposite direction forces 
the body forward in a straight line. 
The physical principles of this motion 

Fig. 150. — Diagram are shown in Fig. 150. In the mOVe- 
illustrating the loco- . /. ,-• n i ,-, -. n i 
motion of a fish. The ment ° f the fish the P alred finS are USed 

tail describes the arc to balance the body and to ascend or 

of an ellipse; the re- degcend m the water> The 'dorsal finS 
suit ant of the two im- 
pulses is the straight guide and steady the body in its progress. 

line in front. The ^ fin ig algQ uged ^ gmde ^ figh> 

Reproduction and development. — The sexes are separate. 
The ovaries of the female lie above the intestine and open 
through the oviducts just behind the anal opening. The 
spermariesof the male communicate with the outside through 
the sperm ducts which open just back of the anus. The 
eggs are extruded from the body and are fertilized by the 
sperms which are set free in the water. The perch does not 




FISHES 



215 



look after its eggs. The young fish live upon crustaceans 
and small worms, but, in turn, may be eaten by larger fish. 
Some fish scoop rude nests out in the gravel in which to 
deposit their eggs and then stand guard over them to pro- 
tect them. The stickleback builds quite an elaborate nest 
for its eggs and the male assiduously cares for them. 

Other Examples of this Class 

Sharks, rays, sawfish, etc. — These examples are repre- 
sentatives of the lowest order of fishes. The sharks are 




Fig. 151. — Hammer-headed shark. Note the five gill slits in the side 
of the neck. 



the lowest in development of the fishes. At the same time, 
they are the fiercest animals of the sea. 

In some sharks the body is protected by spiny processes, 
and in others the body has no protection at all ; but very 
few animals dare to attack them. In general, the skeleton 
is cartilaginous, with no distinct bones as in the higher 



216 



FISHES 



fishes. There may be a deposition of bony matter in cer- 
tain places — for example in the jaws and the vertebral col- 
umn. The jaw is large and strong and furnished with many 
teeth. The mouth of most sharks is on the under side of 
the head some little distance back of the end of the snout. 
Consequently, a shark usually turns on its back when seizing 
its prey The gill openings are from five to seven in number, 

_ on each side of the 
' neck (see the hammer- 
headed shark, Fig. 
151), and are simply 
long, narrow, uncov- 
ered slits. The larg- 
est of all fishes is 
the great baskirg 
shark which attains a 
length of forty feet. 
Some sharks repro- 
duce by eggs which 
are of considerable 
size and furnished 
with a hard chitinous 
shell, often bearing 
several long filaments 
which seem to serve for attachment to seaweeds and the like. 
r In general, a ray, or skate, has a broad, flat body usually 
ending in a long, slender tail (Fig. 152). It swims close to 
the bottom of the sea for the most part, and feeds upon 
crabs, small fish, etc. It does not, like the shark, turn over 
to seize its prey, but swims quietly over a fish and quickly 
settles down upon it, holding it fast with the broad body 
and strong jaws. 




Fig. 152. 



king ray, commonly called 
stingaree. 



FISHES 



217 



Some rays are peculiar in having an electrical organ in 
the body that is capable, in the larger ones, of generating 
enough electricity to disable a man. It is probable that 
this is used in catching prey and in defending themselves 
from enemies. Other rays have long 
spines on their tails with which they can 
inflict serious wounds. These are the 
sting rays (Fig. 152). 

The sawfishes, which belong to the 
ray family, have long, sharklike bodies 
with the snout prolonged into a flat, 
horny blade beset with teeth on each 
side (Fig. 153). This saw varies from 
four to six feet in length and ten to 
twelve inches in width. It constitutes 
a formidable weapon against its enemies. 
The sawfishes are found off the coast 
of Florida and in tropical seas farther 
south. 

Sturgeons, gar pike, etc. — The orders 
of fishes represented by the sturgeons, 
gar pike, spoonbill catfish, and bowfin 
seem to stand between the sharks and 
rays on the one hand and the bony fishes 
on the other. These few fishes, known 
as the ganoids, are the remnants of a 
host of similar fishes that lived in the 
Devonian and Carboniferous ages. They are notable for 
the bony plates that arm the outside of the body instead 
of the flexible scales on the bony fishes. Also for the 
lunglike structure and function of the air bladder. The air 
bladder in some ganoids connects with the gullet by an 




Fig. 153.— Saw of a 

sawfish. 



218 FISHES 

open duct. Moreover, the air bladder is furnished with an 
unusual amount of blood and undoubtedly acts more or 
less as a lung, for both the gar pike and the bowfin often 
come to the surface, force out bubbles of air, and take in 
a fresh supply. 

The sturgeons, which occur in many of the streams and 
lakes of the northern hemisphere, are the largest of the 
fresh- water fishes. Those of the lower Columbia River 
attain a weight of eight hundred to one thousand pounds. 
The skeleton, for the greater part, is cartilaginous with 
no small bones in the flesh. The body has five rows of 
large bony plates on the outside, but they are not contiguous 
and do not form a complete covering. The relish, caviar, 
is made from the roe or egg mass of sturgeons. 

The gar pike, also known as the long-nosed gar, or bill- 
fish, is common in the United States, in lakes and rivers, 
from Lake Champlain to Texas. It has a long, slender 
body accentuated by a long, slender beak, composed of the 
two jaws, each of which is armed with teeth. It approaches 
the bony fishes in many respects. The body is covered 
with bony scales forming a complete armor and the skeleton 
is bony. It attains a length of about five feet. 

Bony fishes. — The members of this order of fishes are 
distinguished from the preceding types by several charac- 
ters chief among which is the possession of a bony skeleton. 
Indeed, this characteristic has given them the distinctive 
appellation of bony fishes. This order furnishes our most 
important food fishes, such as the herring, cod, salmon, 
mackerel, halibut, etc. 

The mackerel is one of the most important food fishes. 
It is found from Labrador to North Carolina. They come 
in great schools, quite regularly in May and June of each 



FISHES 



219 



year, to the waters along the coast to spawn. At this time 
they are lean and not in good condition for catching. After 
spawning, however, they commence to move northward 




Fig. 154. — Mackerel. 

along the coast and at the same time begin to grow fat 
(Fig. 154). 

The common herring (Fig. 155) is found on both sides of 
the Atlantic. On our coast it extends in abundance from 
Greenland to Massachusetts. The herring, like the mackerel, 



%$8ton^ 



L} ^^^kl... 





Fig. 155 — Herring. 

lives in deep water during the winter season, but comes 
to the coasts, in the spring, to spawn in shallow water. 
They come in immense shoals and at this time are 
caught in great numbers, in nets, off the coasts of 
Newfoundland and Labrador. 



220 



FISHES 



Of nearly equal importance with the mackerel and herring 
is the cod. Cod are found from Cape Hatteras to the 
Arctic Ocean, but are especially adapted to cold waters 




Fig. 156.— Cod. 



and are most abundant in the northern seas. The cod 
weighs anywhere from ten to one hundred and fifty pounds 
and sometimes more. They are exceedingly voracious and 
live largely on other fish, especially herring (Fig. 156). 




Fig. 157. — Chinook salmon. 



The salmon are anadromous fishes. That is, they live 
in the sea, but ascend rivers to spawn. The chinook (Fig. 
157) salmon begins running up the Columbia River as early 
as March. The first ones to enter the river travel slowly, 



FISHES 221 

but may finally reach the smaller tributaries of the river 
over a thousand miles from the sea. Here, on beds of 
fine gravel, they deposit their eggs. An individual salmon 
spawns only once, and as soon as the spawning is done 
it is believed the males and females die. 

"The game fish which has been most written about and 
which is, perhaps, best and most widely known among the 
anglers of the world is undoubtedly the brook trout or 
speckled trout." It belongs to the salmon family and in- 
habits cool, clear, and woody streams in the eastern part of 
Canada and our northern states, but is fast disappearing. 

In addition to the fishes especially mentioned in the fore- 
going paragraphs, there are many others that form a very 
important part of our food supply. The perches, pikes, 
basses, anchovies, sardines, bluefish, halibut, mullets, and 
others are familiar food fishes. The black bass is an ex- 
cellent food and game fish and is widely distributed in the 
streams and lakes of the eastern United States. The red 
snapper and the pompano are very important food fishes, 
especially along the Gulf coast. The sheepshead, so well 
known along the Atlantic and Gulf coasts, is a game fish 
and is of great commercial importance. 

There are something over sixty species of the bony fishes 
that constitute the family of flying fishes. They are found 
in nearly all warm seas, usually appearing in schools near 
the surface of the water and sailing, or flying through the 
air. The largest species is found off the coast of southern 
California. This is the only flying fish inhabiting our Pacific 
coast north of Cape San Lucas. It is the largest flying 
fish known, attaining a length of eighteen inches and has 
the greatest power of flight of any member of the group. 
These fishes are enabled to sail through the air by means 



222 



FISHES 



of the greatly elongated and enlarged pectoral fins (Fig. 
158). By means of vigorous, quick strokes of the tail and 
enlarged tail fin, the fish is able to jump from the water 
into the air. Then the large pectoral fins are spread and 
the fish floats on the air somewhat as a man borne by a 
parachute. It is asserted that some of the larger species 




Fig. 158. — Flying fish. 



actually vibrate the pectoral fins, thus producing a real 
flight capable of prolonged duration. 

The bony fishes, for the most part, have large, conspicuous 
eyes, without eyelids, but covered with a thin, transparent 
skin. There are some, however, that five in the caves and 
underground streams of Illinois, Indiana, Kentucky, 
Tennessee, and Alabama, that have rudimentary eyes, — 
so rudimentary that in two or three species, at least, they 
are wholly valueless as organs of vision. The bodies of 
these fishes are colorless and translucent. One species 
lives in the Mammoth Cave of Kentucky. 

The eels are bony fishes with long, cylindrical bodies 
bearing small inconspicuous scales. The common eel 
(Fig. 159) is found on both coasts of the Atlantic and in 
the rivers, lakes, and streams of the eastern United States, 



FISHES 223 

from the Gulf of St. Lawrence to Texas and Mexico. Their 
habits are imperfectly known, but this much seems true. The 
young eels are born in the sea from eggs deposited by the 
mature female. In the spring these young eels ascend the 
rivers and streams, in which they remain until they are two 
or three years old. When grown and ready to spawn, 
they return to the sea. 




Fig. 159. — Eel. 

The electric eels, so-called, belong to another order of 
fishes. They are eel-like in shape but are not true eels. 
They possess powerful electric batteries. 

Lung fishes. — All of the sharks, rays, and bony fishes 
breathe by means of gills. The air bladder, w T hen present 
in these fishes, seems to function only as a hydrostatic 
apparatus. But in the ganoids, represented by the bowfin, 
gar pike, sturgeon, and spoonbill, the air bladder certainly 
functions, to some extent, as an organ of respiration. So 
we find that the ganoids foreshadow, as it were, fishes which 
possess true lungs in which the blood is purified by the ex- 
change of gases. There are, at least, three very interesting 
species of fishes, known as the lung fishes, in which the air 
bladder is modified into a fairly well-developed lung. One 
species is found in the fresh waters of Queensland, Australia, 
and is called Ceratodus, or " Burnett Salmon." It grows 



224 FISHES 

to the length of four or five feet, and the body is covered 
with scales (Fig. 160). It has gills like other fishes, but, 
in addition, the air bladder is modified into a respiratory 
organ that opens into the pharynx, like the lungs of mam- 
mals. The blood flows to this lung and is there purified 
exactly as in the higher animals. The Ceratodus lives in 




Fig. 160. — Australian lung fish. 

still pools that become very stagnant during the dry sum- 
mer season, and it survives only by rising to the surface 
now and then to take fresh air directly into the lung. 

Of the other lung fishes, one species lives in West Africa 
and one species is found in the rivers of South America. In 
both of these species the modified air bladder, or lung, is 
divided into two lobes, and in this respect they differ from 
Ceratodus. The walls of each lobe are supplied with many 
blood vessels filled with venous blood which is brought to 
the lung by a special pulmonary artery to be purified. The 
species in West Africa also fives in pools which dry up during 
the hot season. Before the water wholly evaporates the 
fish descends into the mud and hollows out a place in which 
it lies until the rains come again. 

General character of fishes. — For the first time we now 
meet with animals that have a jaw bone and bony skeleton. 
The skeletons of all fishes are not bony, for some have 
cartilaginous skeletons. Moreover, the fishes have a true 
skull, which, however, in some is rather rudimentary. The 



FISHES 225 

brain of fishes is well developed and the blood is red but 
cold. They have a true but single heart consisting of an 
auricle and ventricle. Most fishes breathe only by means 
of gills. The gills vary in number and structure in different 
orders, but are alike in their general structures in the bony 
fishes, of which those described in the perch may be taken 
as an example. 

Habits and adaptation to environment. — Fishes are 
preeminently adapted to an aquatic life, and all live in the 
water. The body, in most cases, is of such a form that it 
"cuts" the water and thus offers the least resistance. 

For obtaining air from the water, all fishes are furnished 
with some kind of gills. This is a direct adaptation to their 
environment. Again, the fishes are quite large animals and, 
for the most part, are very active. Consequently, there is 
a great deal of the tearing down and building up processes 
going on in the body. As a result, there must be some adap- 
tation or arrangement whereby the blood may have free, 
constant, and full access to air. To provide for this we have 
already seen how the mouth, pharynx, and gill covers are 
so constructed that a current of fresh water, laden with air, 
is kept constantly flowing over the gills. Moreover, the 
gills are not of one piece, but are composed of a great number 
of filaments to provide more space whereby the blood may 
come in contact with more water. Again, the limbs of 
fishes, if the fins may be called such, are admirably adapted 
for locomotion in the water, but totally useless on land. 

Some fishes are protected from their enemies by their 
resemblance to objects in the sea. One of the anglers is 
said to counterfeit very remarkably a rock with its attached 
growth of seaweed and sea animals. Undoubtedly this 
resemblance also serves as a ruse for capturing its prey. 

herrick's zool. — 15 



226 FISHES 

Some fishes are clothed with spines as a protection from 
their foes. Others are found in company with certain 
jellyfishes where they receive the protection of the stinging 
cells. Others creep within the shells of certain mollusks. 
Among the bullheads and catfish, the first ray of the dorsal 
and pectoral fins is developed into a sharp, stiff, serrated 
spine which inflicts severe wounds. In the members of 
two genera of this family of fishes a poison gland is con- 
nected with the pectoral spine. 

Economic importance of the fishes. — The commercial 
importance of this group of animals is very great. The 
place that the fishes fill in the food supply of the American 
people is so important that the United States government, 
long ago, established the United States Fish Commission 
(now called the Bureau of Fisheries) and annually appro- 
priates large sums of money to enable the members of this 
commission to study the habits, distribution, food, and 
methods of preservation of our most important food 
fishes. The fast-failing supply of many of our most im- 
portant food fishes has caused the government to establish 
extensive fish hatcheries at favorable locations. From 
these hatcheries thousands of young fish and eggs are sent 
to the different ponds, lakes, and streams of the United 
States and even the oceans bordering this country. For 
example, the cod is propagated artificially on a more ex- 
tensive scale than any other marine fish. The number of 
cod fry liberated by the United States Fish Commission 
in 1905 was 169,577,000. The common whitefish may be 
taken as an example of the work done by the Commission 
in maintaining the supply of fresh-water fishes. In the 
fiscal year of 1905 the United States Fish Commission 
hatched and planted 268,405,000 whitefish fry. 



FISHES 



227 



The cod fishery employs more men and more vessels 
than any other fishery in the United States. There are 
hundreds of vessels and thousands of men employed in 
catching cod. The annual catch amounts to more than 
ninety-six million pounds, with a first value of about two 
million dollars. 

The herring fishery is also very extensive. These fishes 
go in immense shoals, a single shoal sometimes covering 
several square miles and containing two or three billion 
individuals. It is estimated that between one and two bil- 
lion pounds of herring are taken every year. 

The annual value of the salmon taken on our Pacific 
coast, including Alaska, exceeds thirteen million dollars. 
The two species, chinook and blueback, comprise the 
greater portion of the catch represented by this Vast 
amount, the catch of the other three species being insig- 
nificant in comparison. 

The common whitefish which is an in- 
habitant of the Great Lakes region, from 
Lake Superior to Lake Champlain, furnishes 
a food product valued at nearly three 
million dollars a year. 

The New England catch of mackerel 
amounts to about six million pounds, valued 
at about four hundred thousand dollars, and 
sixteen thousand barrels salted, valued at 
one hundred and eighty thousand dollars. 

The halibut, menhaden, anchovy, sardine, 
trout, red snapper, pompano, sturgeon, blue- 
fish, and scores of others swell the aggre- horse. 
gate value of the food fishes of America to almost fabulous 
figures. 




228 FISHES 

CLASSIFICATION OF THE EXAMPLES 

Class — Pisces. 

Subclass — Elasmobranchii. 

Order — Selachii. 

Types of Order. 

Sphyrna zygcena — Hammer-headed shark. 

Raja erinacea — Ray. 

Carcharhinus glaucus — Blue shark. 

Trygon sabina — Sting ray. 

Torpedo occidentalis — Electric ray. 

Pristis pectinatus — Sawfish. 

Subclass — Teleostomi. 

Order — Chondrostei. 

Types of Order. 

Acipenser sturio 1 ~ 

. . , . , \ Sturgeons. 

Acipenser rubicundus j 

Scaphirhynchus platyrhynchus — Shovel-nosed 

sturgeon. 

Order — Holostei. 

Type of Order. 

Lepidosteus osseus — Gar pike. 

Order — Teleostei. 

Types of Order. 

Oncorhynchus tschawytscha — Chinook salmon. 

Gadus callarias — Cod. 

Clupea harengus — Herring. 

Scomber scombrus — Mackerel. 

Anguilla chrysypa — Eel. 

Cypsilurus calif ornicus — California flying fish. 

Perca flavescens — Perch. 

Subclass — ■ Dipnoi. 

Order — ■ Monopneumona. 

Type of Order. 

Ceratodus forsteri JS> - Lung fish. 

Order — Dipneumona. 

Types of Order. 

Protopterus annectans ) T _ . 

T . f . , r Lung fishes. 

Lepidosiren paradoxa. J 



XX. FROGS, TOADS, AND SALAMANDERS 

Chordata (continued) 

Class III. — Amphibia (animals with double lives), (amphi, 
double; bios, life) 

As a class, the amphibians, of which there are over a 
thousand known species, present a great diversity of forms. 
No general statement can be made regarding this class of 
animals to which exception cannot be found. The great 
majority of the amphibians possess legs and have smooth 
skins — not covered with scales like the snakes and lizards. 
A typical amphibian lives a double life, as it were. It 
begins life in the water, in the form of a fishlike animal 
without legs but with a large tail and a pair of external 
gills. Later, the gills are replaced by lungs, the tail is 
absorbed into the body, and four functional legs appear. At 
this stage of its existence one species of amphibian may 
live on land while another species may confine itself wholly 
to an aquatic life. 

An Example of the Class — the Green Frog 

The body. — The body of the frog is short and wide and 
without a tail. It is divided into two regions only, — the 
head and the trunk. Like the perch, there is no distinct 
neck, yet there is one neck vertebra between the head and 
trunk which shows that the neck of the higher vertebrates 
is just beginning to make its appearance in the frog. The 



230 FROGS, TOADS, AND SALAMANDERS 

body of the frog is covered with a smooth, moist, clammy 
skin devoid of scales. The color of the skin usually accords 
with the surroundings and may change to suit new environ- 
ments. The color is due to cells of pigment in the skin. 

Eyes. — The two eyes are very prominent and protrude 
from the head. Each one is furnished with an upper and 
an under lid. The upper lid is thick and not capable of 
much movement, but when the eye is withdrawn, this lid 
drops down over it in a sort of mechanical way. The under 
lid is thin and can be drawn over the eye. It is called the 
nictitating membrane. 

The hearing organs. — Back of each eye is a conspicuous, 
round area, the eardrum or tympanum. An elastic rod, 
the columella, one end of which is attached to the inner 
surface of the tympanum, extends to the inner ear situated 
within the skull. When sound waves strike the tympanum 
and cause it to vibrate, the vibrations are transmitted by 
the rod to the inner ear, which is the true organ of hearing. 
Each ear communicates with the mouth through the Eusta- 
chian tube. 

The nostrils and manner of breathing. — In front of the 
eyes and above the mouth are the two nostrils. Each 
opening is furnished with a valve so that it can be tightly 
closed. Both nostrils communicate directly with the mouth. 

Within the body cavity of the frog are two pink-colored 
lungs of considerable size that communicate with the mouth 
through the windpipe. They are filled with air spaces, 
surrounded with walls permeated with capillaries containing 
blood. It must be noted, however, that the lungs of the 
frog are not perfect organs of respiration and are aided in 
this work by the skin and the mucous membrane of the 
mouth and pharynx. 



FROGS, TOADS, AND SALAMANDERS 231 

Air is taken into the mouth through the nostrils which 
are then shut by means of the valves. At this time the 
floor of the mouth is bulged downward, showing that the 
mouth is full of air. By an action similar to that of swal- 
lowing, in which the floor of the mouth is raised, the air 
is now forced into the lungs. The air is expelled from the 
lungs by the contractions of their walls aided by the mus- 
cular contractions of the walls of the abdomen. 

The skin is furnished with many minute blood vessels 
and aids in the process of respiration. 

The mouth and tongue. — The mouth of the frog is large, 
and the jaws can be opened very wide. There is a row of 
small teeth on the upper jaw and a few on the roof of the 
mouth but none on the lower jaw. These serve merely to 
hold the prey, not to masticate the food. 

The tongue is attached to the mouth by its anterior end, 
thus leaving the posterior end free. This arrangement 
enables the frog to extend its tongue outside of the mouth 
nearly its w T hole length, since it is attached at the front part 
of the mouth. The tongue is covered with a sticky, mucous 
secretion. 

Legs and locomotion. — The frog has four well-developed 
legs, the hind pair being much the longer and stronger. 
The thighs of the hind legs are furnished with strong muscles 
and the hind feet are long, broad,' and webbed. 

The frog has three methods of locomotion — walking, 
swimming, and leaping. Under certain conditions — for 
example, when climbing up a sharply inclined surface — this 
animal moves in a slow, awkward walk. Its main method 
of locomotion on land is by long and powerful leaps with 
the hind legs. In water the frog is a model swimmer. 
The front legs take no active part in this method of loco- 



232 



FROGS, TOADS, AND SALAMANDERS 



motion, the body being propelled by the powerful strokes 
of the hind legs aided by the webbed feet. 

Alimentary canal. — The mouth opens into the wide 
gullet which, in turn, leads to the long stomach. The 
stomach narrows posteriorly into the intestine, which makes 
several turns and ends in an expanded portion, the cloaca 
(Fig. 162). The kidneys, oviducts, and bladder open into 
the cloaca. The lobed liver communicates with the an- 

Bac J^bone Oviduct Spinal cord_^£ ra i n 

-'longm 




Liver 
Pancreas 

Fig. 162. — Internal structure of a frog. 

terior part of the intestine through the duct of its gall 
bladder. A pancreas is also present, the duct of which 
opens into the duct of the gall sac. 

Excretory organs. — There are two reddish brown kid- 
neys lying on the dorsal side of the body cavity near the 
cloaca. Each one opens into the dorsal side of the cloaca 
through a tube, the ureter. The bladder is found on the 
ventral side of the cloaca (Fig. 162). The lungs and skin 
do their share of excretion by getting rid of the carbon 
dioxide from the blood. 

The circulation of the frog. — The frog has a closed cir- 
culation and the heart is the principal organ of the circu- 



FROGS, TOADS, AND SALAMANDERS 233 

latory system. It is composed of three principal parts, 
the muscular ventricle and two thin -walled auricles. The 
blood is sent out from the anterior end of the ventricle 
through a single artery, which gives off three branches on 
each side. Four of these pass to different parts' of the body 
and end in capillaries The capillaries unite to form veins 
through which the blood returns to the right auricle of the 
heart. Of course this blood is impure and charged with 
carbon dioxide. The remaining two branches carry blood 
to the lungs and skin, where it is purified and returned to 
the left auricle. The auricles empty their blood, both pure 
and impure, into the ventricle. But by a complicated 
system of valves and by the manner in which the single 
artery branches the two kinds of blood mix but little and 
the purest blood is sent to the head, the next best to the dif- 
ferent parts of the body, and the impure back to the lungs. 

The food and method of obtaining it. — The frog feeds 
upon living, moving animals only; as worms, moths, flies, 
beetles, etc. These are caught, while they are in motion, 
on the end of the tongue as it is darted from the mouth with 
great rapidity. The sticky, mucous secretion on the tongue 
serves to hold the prey. The food is swallowed whole and 
digested at leisure. 

Reproduction and life history. — When mature, the eggs 
are set free in the body cavity and finally find their way into 
the mouths of the oviducts. In the passage through the 
oviduct each egg becomes coated with a gelatinous ma- 
terial which swells greatly when the egg reaches the water. 
The eggs are deposited in large, irregular, jellylike masses, 
usually near the edges of pools and ver}^ often about the 
stem of some plant (Fig. 163). After a number of warm 
days each egg hatches into a black, wiggling object with an 



234 



FROGS, TOADS, AND SALAMANDERS 




Fig. 163. —Eggs of frog. 

indistinct head and a wide tail. This form is known as a 
"tadpole," or "polliwog." The tadpole lives in the water 
attached, part of the time at least, to the jellylike mass 

or to water plants, by an 
adhesive apparatus, or 
" holder " on the head 
near the mouth. A little 
later, the tadpole becomes 
a free-swimming organism. 
It breathes by means of 
small external gills on 
each side of the head 
(Fig. 164), and eats mi- 
nute particles of vegetable 
matter found in the water. 
Later, the external gills 
disappear and are replaced 
by internal ones. After 
some time, the hind legs 
begin to appear and then 
the front legs, while, at the 

Fig. 164. Tadpole, h dfied, SEme tim 6, the tail becomes 

and showing gills {A). shorter and shorter. In 




FROGS, TOADS, AND SALAMANDERS 235 

the meantime the gills disappear and lungs begin to form. 
Finally, the legs and lungs become fully developed; and 
the tail wholly disappears. The frog is then considered 
an adult. Some frogs pass through these changes in one 
season, but the green frog usually passes the first winter as 
a tadpole and completes the changes the following summer. 

Habitat and habits. — The frog is found near ponds, pools, 
or streams of water. In a quiet walk along the banks of 
a stream, they may be seen leaping into the water from their 
resting places in the grass, where they have been in search 
of food. They are obliged to remain near the top of the 
water in order to obtain air and usually float at the surface 
with the head out of the water. In spring they become 
very musical and congregate in ponds to lay their eggs. 
After the eggs are laid they scatter to different places to 
avoid overcrowding and to insure a food supply. In the 
winter they dive to the bottoms of ponds and burrow into 
the mud. Here they pass into a state of stupor, with the 
eyes closed, and the organs of the body inactive. In this 
condition they are said to be hibernating. 

The common toad. — The toad differs from the frog by 
the total absence of teeth, by the rough, warty skin, and 
by the fact that it lives on land, going to the water only in 
the spring to lay its eggs. It must be said, however, that 
toads require damp, moist places in which to live. They 
are often seen in great numbers after a shower because they 
delight in a cool, moist atmosphere, and come out from their 
hiding places to enjoy it. They usually remain hidden 
during the day and come out at dusk and at night to 
catch insects in the same manner as the frog, for the tongue 
of the toad is similarly constructed. The alimentary canal, 
excretory and circulatory organs are similar to those of the 



236 FROGS, TOADS, AND SALAMANDERS 

frog. The life history of the toad is like that of the frog 
except that the eggs of the toad are deposited in long, 
coiled strings in shallow water. The eggs are black and 
spherical and are held together and surrounded by a string 
of transparent gelatinous material. 

Molting of the toad. — From time to time, in its life, a 
toad sheds its skin much after the manner of a molting 
caterpillar. "Without any preliminary symptoms or loss 
of appetite or liveliness, the body makes a few twisting 
motions, the back is now and then curved, and the skin 
splits down the middle line." After the skin has been 




Fig. 165. — Surinam toad. 



partly peeled from the body, the toad gets the free end into 
its mouth, gradually slips out of the skin backwards, and 
finally swallows it. The new skin is usually light in color 
and is wet and shining but soon becomes dry and hard. 



EROGS, TOADS, AND SALAMANDERS 237 

Hibernation. — When the toad feels winter coming on, 
it digs a hole in the earth with its hind feet — backing into 
it as it digs — and lies at the bottom, in a deep sleep, until 
spring returns. 

Toads with interesting habits. —The Surinam toad which 
lives in Dutch Guiana, South America, is exceedingly in- 
teresting because of the remarkable manner in which its 
eggs are cared for and hatched. Just previous to the egg- 
laying period, the skin of the back of the female is specially 
prepared by nature for a remarkable proceeding. It be- 
comes very thick, spongy, and soft. The male then 
spreads the eggs over the back of the female, where each 
egg becomes surrounded and finally enclosed in a pouch 
produced by the skin growing up around it. The 
opening of the pouch is closed by a lid of skin. Here 
the eggs remain until they are fully incubated, the tad- 
pole stage is passed, and a tiny but perfect toad 
emerges from the skin of its mother's back! Therefore, 
the Surinam toad does not pass its larval life in the 
water, but in the adult stage it is thoroughly aquatic 
and has the hind feet webbed (Fig. 165). 

Other Amphibians 

The caecilians. — These are the lowest of the amphibians. 
They are wormlike in appearance and bear little resemblance 
to vertebrates. They have no legs or fins and many of them 
are blind, with the eyes hidden beneath the skin. They 
inhabit the tropical regions of Mexico, Central and South 
America, Africa, Asia, and Australia, but none are found 
in the United States. These amphibians are of burrowing 
habits and possess strong, solid skulls because they burrow 
entirely with their heads. 



238 



FROGS, TOADS, AND SALAMANDERS 



Necturus. — The necturus has a long, rather depressed 
body, reminding one of a reptile. It is found in the rivers 
of the upper Mississippi Valley and in the Great Lakes and 
the lakes of central New York. The body reaches a maxi- 
mum length of sixteen inches and has two pairs of short 
legs. It has three bushy red gills on each side of the head 
and is especially to be noted as an amphibian that retains 
its gills throughout life. 

The siren, or "mud eel," which is found abundantly in 
the ditches of the South Carolina rice fields and in fact 




Fig. 166. — Mud eel or siren : G, gills. 



occurs throughout the southern states to Texas, is another 
amphibian that retains its gills throughout life. It has a 
dark-colored, cylindrical body about two feet long, but 
has only one pair of limbs, the front pair (Fig. 166). 

Hellbender. —The " hellbender," " water dog," or "alli- 
gator," as it is variously called, is a large amphibian 



EROGS, TOADS, AND SALAMANDERS 239 

from eighteen to twenty inches long, found in the Ohio 
River and its tributaries. It is a repulsive but harmless 
animal. Closely allied is the giant salamander of Japan, 
which attains a length of three feet. 

The congo snake. — There is an amphibian found in the 
swamps, muddy streams, and ditches of the southeastern 
states that is known as the "congo snake" or "congo eel." 
It has a slender, eel-like body about two feet long with two 
pairs of small, short legs. It is erroneously thought to be 
venomous. 

Salamanders. — The salamanders are small, smocth- 
skinned, reptile-like amphibians found in many and varied 




Fig. 167. — Spotted salamander. 

situations all over the United States. They differ from 
the toads and frogs in possessing tails that persist through- 
out life. The spotted salamander, which has a series of 
round yellow spots along each edge of the back, is about 
six inches long, and is common in the eastern United 
States (Fig. 167). It is terrestrial, frequenting moist 
places beneath logs, leaves, etc. Like the toad, it passes 
through remarkable changes in its development, — the 
young possessing gills. The adult, when disturbed or 
handled, may eject a stream of transparent fluid. 



240 FROGS TOADS, AND SALAMANDERS 

Some of the members of the salamander group are 
known as newts. The small red-spotted newt when 
grown frequents ditches and lays its eggs in water, but 
lives nearly three years in an immature form on land in 
moist places. Some salamanders are aquatic and some 
terrestrial. Those living in water have flattened tails, 
while the terrestrial forms have cylindrical tails. 

Most of the land salamanders bring forth their young 
alive, while those inhabiting the water lay eggs which are 
usually attached to a submerged plant stem. 

Frogs. — The most common frogs in the United States 
are the bullfrog, green frog, and the leopard frog. Of 
these, the green frog is probably the most familiar, al- 
though, in many localities, the leopard frog may be more 
common. The cheerful and industrious croakings of these 
frogs may be heard in the spring issuing from every swamp 
and pond in the neighborhood. Many frogs pass the win- 
ter deep in the mud at the bottoms of pools. 

The bullfrog is so well known that it hardly needs de- 
scription. It is noted for its large size and great, thick 
thighs which furnish such tempting delicacies for epicures. 
It varies from five to six inches in length and has a deep 
bass voice. 

The bullfrog is always found near water into which it can 
jump when disturbed. On the other hand, the little wood 
frog, which is only about one and a half inches long, lives 
in the woods and depends for safety upon its resemblance 
to dead leaves. It can leap several feet at a time, but is 
soon exhausted by its efforts and is easily captured. 

Tree toads. — We have in the United States several 
species of amphibians known as tree frogs and tree toads. 
As a matter of fact, these little animals belong neither to 



FROGS, TOADS, AND SALAMANDERS 



241 



the family of true toads or frogs but fall in a family by them- 
selves. The tree toads (Fig. 168) of our country are noted 
for their loud voices. It is these that we hear piping so 
shrilly in the early 
spring. In the even- 
ing, after a rain, the 
loud, clear piping of 
the little tree toad, 
known as Hyla versi- 
color, is almost in- 
variably heard. It 
is called versicolor, 
because, like many 
other tailless amphib- 
ians, it possesses the 
power of changing 
the shade, or tint of 
its skin. Ordinarily, 
it is gray above 
with dark, irregular 
blotches, greatly re- 
sembling the bark of 
trees (Fig. 169), on 
Which it lives. On 
the under sides of all of its toes and fingers are small 
adhesive disks by which it is enabled to cling to the trunks 
and branches of trees. It is also able to leap two or three 
feet from branch to branch. 

Characteristics of the group. — To sum up, the Amphibia 
are animals that, in general, live a double life. That is, 
one part of their lives, the first part, is passed in the water, 
with few exceptions, while the later, or adult stage, is usually 

herrick's zo'ol. — 16 




168. — Tree toad (Hyla versicolor) . 
the suction disks on the toes. 



Note 



242 



FROGS, TOADS, AND SALAMANDERS 



passed on land. Since the early, or larval stage, of these 
animals is passed in the water, most of the larvae are furnished 
with gills for breathing. Some amphibians that live in the 
water all their lives retain the gills throughout life. Those, 

however, that live on 
land during the adult 
stage lose the gills, and 
have lungs instead. 
They differ from the 
fishes in having seg- 
mented limbs instead 
of fins. They are 
cold blooded. The 
ma j ority have smooth, 
scaleless skins. 

Adaptations to en- 
vironment. — Note 
that the tadpoles of 
amphibians which live 
in the water have 
gills to suit such an 
environment, but when dry land is substituted for water, 
the gills are lost and lungs appear. Again, the necturus 
and the siren that live in the water all their fives retain the 
gills throughout life, as best suited to such an environment. 
Tadpoles of frogs and toads are provided with broad, 
flat tails for swimming; but the adult frogs and toads are 
tailless. Many frogs are excellent swimmers, however, 
because of their webbed toes and the adaptations of their 
legs to such a purpose. The webbed toes of some species 
of the tree frogs of the Malaysian Islands (Fig. 170) have 
become much enlarged and adapted to quite a different 




Fig. 169. — Tree toad on the bark of a tree. 



FROGS, TOADS, AND SALAMANDERS 



243 



purpose; namely, that of parachutes to aid in their leaps 
from branch to branch. The little tree toad of our country, 
of which we have spoken, has its toes and fingers provided 




Fig. 170. — Malaysian tree frog. 

with adhesive disks which enables it to cling to vertical 
surfaces and, hence, adapt it to an arboreal life. 

Relationship and significant features of this branch. — 
The Amphibia are a group of animals standing between the 
fishes and the reptiles. The fishes, on one hand, are water 
animals ; the reptiles, on the other hand, are land animals ; 
while the amphibians, in between, are both. That is, the 
greater number of them live in water during the first part 
of their lives, and on land, the latter part. 

The Amphibia within themselves are very interesting, as 
showing a gradual transition from water-breathing to air- 



244 FROGS, TOADS, AND SALAMANDERS 

breathing animals. The lower of the amphibians — the 
necturus and the siren — pass their entire lives in the water 
and possess gills in the adult stages. The higher amphibians 
— toads and frogs — live on land in the adult stage, and 
possess lungs. 

Among the so-called salamanders, there is, at least, one 
species that, within its own lifetime, may pass in transition 
from the lower to the higher types of the Amphibia. That 
is, the individuals of this particular species of salamander 
may, under stress of circumstances, change from a form that 
possesses external gills and is fitted for an aquatic life to a 
form that possesses lungs and is fitted for life on land. In 
either of these stages, this amphibian, the axolotl, breeds 
successfully and reproduces its kind. When in the aquatic 
form, the axolotl has the structure, habits, and habitat of 
the lower amphibians; but when it assumes the land form, 
it has the structure, habits, and habitats of the higher 
amphibians. This remarkable twofold life is evidently an 
adaptation to the environment of this animal. When the 
ponds in which it lives are about to dry up, it assumes 
the land form, and in this stage it has long been known as 
the spotted salamander. 

Economic importance of the Amphibia. — As a group, 
the Amphibia are not of great economic importance, for 
there are only two species that are considered to possess 
any significant economic value, namely, the bullfrog and the 
toad. The bullfrog may be found in season in the markets 
of all of our large cities. In France and in southern Europe, 
the European green frog is reared in "froggeries" and used 
extensively as an article of food. From a purely agrarian 
point of view the common toad has a greater economic 
value than any other amphibian. 



FROGS, TOADS, AND SALAMANDERS 245 

The toads eat only living, moving insects, centipeds, sow 
bugs, etc. They destroy great numbers of noxious insects 
in gardens and fields. Professor Kirkland found by 
examining the stomachs of many toads that "a single toad 
in one season might destroy cutworms which otherwise 
would have damaged crops to the extent of $19.88." The 
toad is of conspicuous service to all agriculturists, but es- 
pecially so to gardeners, who should try to collect toads and 
keep them in their gardens. 

CLASSIFICATION OF THE EXAMPLES 

Class III — Amphibia. 
Order — Urodela. 
Types of Order. 

Necturus maculatus — Necturus. 

Siren lacertina — Mud eel. 

Amphiuma means — Congo snake. 

Arribly stoma punctatum — Spotted salamander. 

Megalobatrachus japonicus — Giant salamander. 

Cryptobranchus alieghaniensis — Hellbender. 

Diemyctylus viridescens — Red-spotted newt. 
Order — Anura. 

Types of Order. 

Bufo americanus — Toad. 

Pipa americana — Surinam toad. 

Rana catesbiana — Bullfrog. 

Rana palustris — Marsh frog. 

Rana clamitans — Green frog. 

Rana sylvatica — Wood frog. 

Hyla versicolor — Tree toad. 



XXI. SNAKES, TURTLES, LIZARDS, CROCODILES 

Chord ata (continued) 

Class IV. — Reptilia (creeping animals) 

The reptiles are cold-blooded animals that differ markedly 
from the amphibians in many important respects. The 
life history of a reptile is comparatively simple, for no rep- 
tile passes through the remarkable changes that are char- 
acteristic of most of the amphibians. The majority of 
reptiles possess an outside covering of scales, or horny 
plates, or, in the case of turtles, of a bony box, while am- 
phibians, for the most part, are smooth skinned. Super- 
ficially, some reptiles resemble certain amphibians and vice 
versa, some amphibians are often mistaken for reptiles. 

An Example of the Class — the Six-lined Lizard 

External features. — The body is long, slender, and more 
or less cylindrical. It presents four divisions — head, neck, 
trunk, and tail, all of which are clothed with scales. This 
contrasts quite strongly with the smooth, short, broad, and 
tailless body of the frog. Like the frog, the lizard has four 
legs, but they are more nearly equal in size and none of them 
are fitted for leaping. Each leg terminates in five digits 
furnished with claws. 

The eyes. — The eyes are conspicuous, but they do not 
protrude. Each has an opaque upper and under lid and a 
nictitating membrane. The latter may be drawn completely 

246 



SNAKES, TURTLES, LIZARDS, CROCODILES 247 

over the eye and when not in use, is folded in the inner 
corner of the eye. 

The ears and nostrils. — Posterior to the corners of the 
mouth are the conspicuous tympanic membranes of the ears. 

The nostrils are situated on the anterior end of the head 
and open into the mouth. 

The mouth and teeth. — The mouth is a wide, slitlike 
aperture extending nearly from ear to ear around the an- 
terior border of the head. The jaws are not dilatable like 
those of a snake, but each one is furnished with a row of 
small, conical teeth. On the floor of the mouth is the nar- 
row, fleshy tongue with a forked extremity. 

Locomotion. ■ — Some lizards are very swift of movement 
and quickly scurry out of sight when alarmed. Others are 
sluggish of movement because the legs are weak and unable 
to bear the weight of the body. The digits of the lizard's 
hands and feet end in sharp claws which enable it to climb 
trees and run nimbly along old logs, rails, etc. 

Food and manner of eating. — Lizards live largely upon 
insects which they catch alive in their capacious mouths. 
Dr. Shufeldt gives an interesting account of the manner in 
which the little American chameleon ate a butterfly. He 
says, "I was so fortunate, not long ago, as to catch one in 
the act the instant after he had made a successful spring 
upon rather a large butterfly. The body of the insect was 
in his mouth while the wings were violently flapping the 
sides of the lizard's face. The reptile would clinch his jaws 
together spasmodically two or three times, shutting his 
eyes with a very tight squeeze every time he did so. At last 
his prey was silent, when with a few energetic kicks he tore 
off the creature's wings and disposed of its body sans cere- 



248 



SNAKES, TURTLES, LIZARDS, CROCODILES 



Scales. — The whole body is covered with scales which are 
true epidermal structures. The scales on the dorsal side 
of the head are large and shieldlike. Those on the dorsal 
side of the abdomen are small and hexagonal, while those 
on the ventral surface are large, rectangular in shape, and 
arranged in eight longitudinal rows. The scales on the 
tail are keeled and arranged in regular transverse rows' 
which give a ringed appearance to this organ. 

The digestive system. — The mouth opens into a slender 
gullet which leads to the stomach. Following the stomach 



Glottis 



Oviduct 



cMdnei/ 

Ureter 




Urinary 
bladder 



Fig. 171 . — Internal structure of a lizard. 



is the small intestine, or duodenum, which is more or less 
coiled. The duodenum is succeeded by the large intestine, 
or rectum, which joins the cloaca, the dilated end of the ali- 
mentary canal. A two-lobed liver lies in the anterior part 
of the body cavity and has a gall bladder which empties 
into the duodenum through the bile duct. A pancreas is 
situated in the loop between the duodenum and stomach. 
At the point of union between the small and large intestine, 
the latter is produced into a short, blind sac, the ccecum 
(Fig. 171). 



SNAKES, TUKTLES, LIZARDS, CROCODILES 



249 



Other Members of this Class 
Snakes 

Garter snake. — This small, harmless snake is found 
everywhere in the United States and will serve as a type 
of the snakes. It has a long, cylindrical body, tapering 




Fig. 172. — Garter snake shedding its skin. Note the old loose skin 
just back of the head. 

toward the tail (Fig. 172). The head is fairly distinct, but 
no limbs are present. The body of the snake is covered 
with scales that overlap like those of a fish. They differ 
from those of a fish in being true eoidermal structures. The 



250 SNAKES, TURTLES, LIZARDS, CROCODILES 

scales on the ventral side of the body are large and extend 
transversely across the width of the body. These scales 
are known as scutes. Each scute is attached to a pair of 
ribs and, moreover , is fastened, or hinged at its anterior 
edge, while the remaining portion of the scale is free. The 
scutes are the main organs of locomotion. The free edges 
of the scutes are brought forward and downward, where 
they catch against the irregularities of the surface, and 
when forcibly returned to their normal positions close to 
the ventral side of the abdomen, force the body forward. 
If an individual should be placed on a smooth surface, 
like glass, it would be unable to crawl because no inequali- 
ties of surface would be presented for the scales to push 
against. 

The eyes of the garter snakes have no lids, but are pro- 
tected by the skin that passes over them, which is trans- 
parent and somewhat thickened just over the eyes. The 
absence of eyelids accounts for the cold, stony stare of 
snakes. No external ear is present. In fact, no snakes 
have external ears. 

The tongue is forked, and the two halves of the lower jaw 
are loosely united in front, while the whole jaw is loosely 
hinged to the head by means of an intermediate bone, the 
quadrate. This arrangement allows the mouth to be greatly 
dilated for swallowing its prey. The teeth all point back- 
ward and are for the purpose of holding its prey, and not 
for chewing, because the food is swallowed whole. 

Pythons. — It is said that some pythons reach the ex- 
treme length of thirty feet, but probably twenty feet is 
nearer the average. They are found in the tropical portions 
of Asia, Africa, and Australia. A python has a prehensile 
tail, and by means of this, clings to the branches of trees, 



SNAKES, TURTLES, LIZARDS, CROCODILES 



251 



while the remainder of the body is left free to wrap around 
its prey. Pythons have vestiges of hind limbs. 

The boa constrictor and anaconda are two very large 
snakes that are found in South America. The anaconda is 
said to attain a length of thirty feet. 

True Cobra of India. — With the exception of the rarer and 
larger " king cobra," which also occurs in India, this is the 
most poisonous snake known. However, it is certainly handled 



,,Q 










i--t- ~'f!V."' : 


<\ C3k .-■ .: ,: r™^ 













Fig. 173. — Copperhead. 

with impunity by those strange men of India, the jugglers 
or snake charmers. The fangs and poison apparatus are 
much like those of the rattlesnake except that the fangs 
of the cobra are permanently erect, while those of the rattle- 
snake are erected under excitement. The bite of the cobra 



252 SNAKES, TURTLES, LIZARDS, CROCODILES 

is almost sure death, and thousands of the natives die 
from it yearly. The poison instantly affects the whole 
system and causes great pain. 

Copperhead. — This is a common poisonous snake of the 
United States. It is found from New England to Florida, 
east of the Mississippi, principally in mountainous dis- 
tricts. The head of this snake is copper colored, hence 
the name. Its venom is second in virulence to that of 
the rattlesnake. In the different localities of its range, 
the copperhead is known as the deaf adder, pilot snake, and 
upland " moccasin" (Fig. 173). 

Water moccasin. — The water moccasin stands next to 
the copperhead among the poisonous snakes of the United 
States. It is greenish brown in color with no conspicuous 
markings and attains a length of four or five feet. Its 
body is large and thick and its tail is blunt. Its venom is 
decidedly virulent. It is found from North Carolina to 
Texas. It is aquatic and lives largely on fishes, tadpoles, 
frogs, etc. 

The rattlesnake. — Although there are several species of 
rattlesnakes, the common one (Fig. 174) found from the 
Atlantic coast to the Rocky Mountains will serve as an 
example. Briefly, the rattle consists of several flattened, 
horny rings at the end of the body, which are fastened 
so loosely together that they may be rattled by move- 
ments of the tail. The number of rattles do not ac- 
curately indicate the age of the snake, as some may be lost 
and several added during one season. The venom is a 
straw-colored liquid secreted by two glands situated under 
the skin on the upper jaw. These glands connect with the 
long, slender fangs which are hollow. When the mouth is 
closed, the fangs lie flat against the roof of the mouth ; but 



SNAKES, TURTLES, LIZARDS, CROCODILES 



253 



when the snake strikes, they are erected and thrown for- 
ward. The venom trickles through the hollow fangs and 
flows directly into the wounds made by them. The fangs 
are normally shed every six or eight weeks and renewed 




Fig. 174. — Rattlesnake (Crotalus horridus). 

as often. Therefore, the rattlesnake cannot be rendered 
permanently harmless by the removal of its fangs. Death 
by the bite of a rattlesnake is by no means sure, but the bite 
always causes intense pain. 
The rattlesnakes, 1 water moccasin, copperhead, and har- 
1 The massasaugas are included among the rattlesnakes. 



254 SNAKES, TURTLES, LIZARDS, CROCODILES 

lequin snake constitute the poisonous snakes of the United 
States. 

By far the greater number of snakes in the United States 
are harmless. Among these are the small green snakes 
that live in the grass and are knowD as grass snakes. The 
large, dark brown water snake that is so abundant along 
streams and feeds upon fishes and frogs is a common 
snake of the eastern United States. It is an unpleasant 
and ill-tempered but perfectly harmless snake. The pilot 
snake is one of our largest snakes. It is lustrous black and 
attains a length of five or six feet. The king snake, corn 
snake, and spotted adder, all closely related to each other, 
are rather conspicuous snakes because of their coloring 
and are fairly common. 

Chief characteristics of the snakes. — The bodies are long, 
cylindrical, and covered with scales. The skin is shed at in- 
tervals. The limbs are absent or rudimentary, and the 
mouth is very dilatable. They progress with a gliding 
movement by means of scales on the under side of the 
body. Most snakes lay eggs, but some bring forth their 
young alive. 

Lizards 

Like the snakes, there are several species of lizards in 
the United States, more species being found in the South 
than in the North, and more in the West and Southwest 
than in the eastern parts of our country. 

Blue-tailed lizard. — One of the lizards common to the 
United States east of the Rocky Mountains is known as the 
blue-tailed lizard, and, in some localities, as the " scorpion." 
Above, it is a dark, glossy green, with five yellowish lines 
running lengthwise, and the tail is usually of a brilliant blue, 



SNAKES, TURTLES, LIZARDS, CROCODILES 



255 



hence its name. Sometimes the tail is a reddish green. 
Below, the animal is pearly white. Its body is cylindrical 
and eight or ten inches long. It has four legs, each ending 
in five toes, and the body is covered with scales. Unlike 
the snake, the jaws are not dilatable. 

Alligator lizard. — This lizard is also known as the 
"pine lizard." It is six to eight inches long, earthy brown 




Fig. 175. 



Alligator lizard. In the struggle for existence, part of the 
tail was broken off. 



above, and dirty white beneath, with blue side patches in 
the male (Fig. 175). Its body is covered with scales, which 
on the back are large; and when angered, it elevates these 
scales as a dog does its hair, and rapidly changes its color, 
thus assuming a very militant aspect. If, by chance, the 
tail of this animal is pulled off, it will be renewed. The 
female lays from six to eight eggs in some secluded place 
in a dry tree trunk, stump, etc. 

American chameleon. — This is a small but very beautiful 
and interesting lizard found in the southern states. Its body 



256 SNAKES, TURTLES, LIZARDS, CROCODILES 

is scarcely three and one half inches long, but its tail may 
be six inches in length. It has gained the name chameleon 
from the fact that it can change its color from green to 
bronze brown, with all the varying intermediate shades. 
Its body is covered with delicate minute scales and is 




Fig. 176. — American chameleon. Note the toes. 

furnished with four nimble legs, which end with very long, 
slender toes (Fig. 176). Beneath its neck is a fold of bright 
red skin that makes a very striking appearance when ex- 
panded. 

Old World chameleons. — The true chameleon, of which 
so much has been written, is an inhabitant of the Old 
World. It is found in Africa and Asia along the coasts of 
the Mediterranean Sea. The head is large and angular, 
and the body is compressed, and furnished with a long, 
prehensile tail and with four legs capable of supporting its 



SNAKES, TURTLES, LIZARDS, CROCODILES 257 

weight (Fig. 177). The eyes are large and, to a certain 
extent, each is independent of the other. The tongue is club- 
shaped and can be darted out from the mouth to the extent 
of six or seven inches for the purpose of catching insects 
on its sticky extremity. There are several layers of different 
colored pigments in the skin, any one of which may be 




Fig. 177. — Old World chameleon. 

made to predominate by contracting and masking the 
others. In this way the animal is able to change its 
color. 

The Phrynosoma. — This reptile is found in the western 
part of the United States and is known as the " horned 
toad." The body, barring the tail, somewhat resembles 
that of a toad, but the spinelike scales that occur on the 
head, neck, and tail of the animal indicate its relation to the 
reptiles. The feet and legs are used for running and not 
for hopping. The horned toads show a remarkable adap- 
tation in coloring to soil on which they live. They can be 

herrick's zool. — 17 



258 SNAKES, TURTLES, LIZARDS, CROCODILES 

kept in captivity easily and thrive on a diet of insects 

(Fig. 178). 





- 














Ik 



Fig. 178. — Horned toad from Texas. 



The Gila monster. — There occurs in the southwestern 
part of the United States, especially in New Mexico and 
Arizona, the largest lizard in the United States, the Gila 
monster. This lizard may attain a length of twenty inches. 
Its body is deep black with blotches of orange, and covered 
by hard, rounded tubercles and scales. Recent experi- 
ments have shown it to be poisonous. The poison glands 
are situated in the lower jaw near the anterior end (Fig, 
179). 



SNAKES, TURTLES, LIZARDS, CROCODILES 



259 



Chief characteristics 
of the lizards. — They 
usually possess a cy- 
lindrical and more or 
less elongated body, 
which in most cases is 
covered with scales. 
Four legs are for the 
most part present, 
but often are unable 
to bear the weight of 
the body and there- 
fore push rather than 
carry the animal. 
The mouth, unlike 
that of the snakes, 
can be opened only 
to a normal extent. 
Finally, the jaws are 
furnished with teeth, 
and the food is mas- 
ticated. 




Fig. 179. 



Gila monster. Photograph by 
Shufeldt. 



Turtles and Tortoises 



These are familiar reptiles to most of us, at least. Some 
of them live on land and some of them live in the water. 
The term turtle is more usually restricted to the aquatic 
forms, while the term tortoise is applied, if strictly used, to 
the members of the family Testudinidse, which are strictly 
terrestrial in habits and possess club feet, but with distinct 
toes. 



260 SNAKES, TURTLES, LIZARDS, CROCODILES 

Sea turtles. — We begm with the marine species because 
these comprise the largest forms. Among the sea turtles 
occurring along the Atlantic coast is the great leather-back 
turtle, one of the largest living turtles, which attains a 
length of six to eight feet and weighs nearly a thousand 
pounds. Its bony, boxlike body is covered with a thick, 
leathery skin and the toes are joined together to form pad- 
dles for swimming. Another is the hawktill turtle, which 
is not much over a third as large as the leather turtle. 
The bony box in which it is incased is covered with horny 
scales which furnish the "tortoise shell" of commerce. 
These scales, or plates, peel off when the shell is properly 
heated. 

A third sea turtle is the green turtle. This turtle has 
gained considerable notoriety from the fact that it furnishes 
the basis for that delicious dish, green turtle soup. This 
reptile occurs in all tropical seas, but in our own country 
it is found along the Atlantic coast from the Carolinas 
south, and often weighs as much as eight hundred pounds. 
It lives on the roots of a sea plant known as eel grass or 
turtle grass. In the early summer the female turtle 
crawls on to the sandy shores of islands in the Gulf of Mexico 
or Caribbean Sea and lays, in a hollow which she scoops out 
of the sand, from one to two hundred eggs about the size 
of hen's eggs. When through laying, she covers the eggs 
with sand and slips into the sea. 

Painted turtle. — This turtle is very common in the ponds 
and streams from Canada to the Gulf of Mexico. During 
the winter it hibernates, but it comes forth with the first 
warm days of spring. Its advent is often heralded by shrill 
piping notes. The eggs, laid in a sand bank, are hatched 
by the sun. Above, the plates of this turtle's shell are a 



SNAKES, TURTLES, LIZARDS, CROCODILES 261 

dark brown bordered by a band of yellow. Those on the 
edges are marked with red. 

Snapping turtle. —This turtle (Fig. 180) is found in streams 
and ponds east of the Rocky Mountains, from Canada to 
Mexico. The shell is too 
small for the complete 
retraction of the head 
and tail, consequently it 
defends itself with its 
strong jaws. The snap- 
ping turtle is one of our 
largest inland turtles, 
often attaining a length 
of three feet. 

Soft-shelled turtle. — 
The common soft-shelled 
turtle is found in the 
tributaries of the upper 
Mississippi and in those 
of the St. Lawrence. Its 
toes, like those of the 
foregoing species, are 

° , . . . Fig. 180. — Snapping turtle. 

webbed lor swimming 

because this turtle is distinctly aquatic. The shell is not 

completely ossified, and, moreover, is covered with a soft 

skin. 

Gopher turtle. — The gopher turtle is strictly terrestrial, 
its toes are bound up within the clublike foot, and the 
limbs are fitted for walking. It is common throughout 
the sandy pine regions of the South. The front feet are 
flat and wide, very much like those of a mole, and each ends 
in five strong, flat nails for digging (Fig. 181). When the 




262 



SNAKES, TURTLES, LIZARDS, CROCODILES 



head is retracted the front feet and legs are brought around 
in front and used completely to close the opening in the 
front of the shell. The hind feet are club-shaped and each 




Fig. 181. — Gopher turtle. 

ends in four toe nails. They live in burrows dug in the soil 
to the depth of four or five feet. 

Chief characteristics of the turtles. — The bodies are short 
and stout and incased in a more or less bony box, called 
the shell. The shell consists of two portions, an upper 
portion, the carapace (Fig. 182), and a lower portion, the 
flastron. These are immovably united by the edges, along 
'.he sides, but remain open in front for the protrusion of the 
head and fore legs, and behind, to allow action of the hind 
legs and afford room for the tail. The turtles have no teeth, 
but the horny jaws have sharp, chisel-like edges that form 
a most efficient cutting apparatus. In most cases the head, 
tail, and legs may be retracted within the shell. In most 
turtles the shell is very completely ossified and covered 
with scales. In the soft-shelled turtles, the shell is not so 
bony but remains soft, while in the leather turtle, the soft 



SNAKES, TURTLES, LIZARDS, CROCODILES 



263 



shell is covered with a layer of fatty material which yields 
considerable oil. The sight of turtles is very keen, for they 




Fig. 182. — Turtle's shell : P, lower side or plastron ; C, upper side, 
or carapace. 

possess well-developed eyes. Unlike snakes, turtles are 
furnished with legs. • 



Crocodiles and Alligators 

Only one species of crocodile and one of alligator occur 
in the United States. The crocodiles are rare and are 
found only in the southern part of Florida. The alligators 
are fairly abundant at present although gradually disap- 
pearing and are found only in the southern states. 

Crocodiles. — Crocodiles are found in Florida, West 
Indies, South America, and Africa, notably along the Nile, 



264 



SNAKES, TURTLES, LIZARDS, CROCODILES 



and in Asia. The American crocodile can be distinguished 
from the alligator by its narrower snout. It sometimes 
attains the length of twelve feet. Crocodiles are ferocious 
and kill many large animals which are seized by the snout 
as they come down to the water to drink. 

Alligators. — Like the painted turtle, the alligator spends 
much of the day lying along a log basking in the sun, 





A 












^ 





Fig. 183. — Young alligator. 



ready to slip into the water at a moment's notice. Alliga- 
tors are exceedingly active in the water and live upon 
animals that come to the water to drink and upon fish. 
They always drag their prey beneath the water and drown 
it. The passage leading to the lungs is closed by a peculiar 
arrangement at the base of the tongue, so that no water 



SNAKES, TURTLES, LIZARDS, CROCODILES 265 

can enter the lungs. These animals come to the surface to 
get air, and the tip of the snout where the nostrils open may 
often be seen projecting just above the water for this purpose. 

In the spring season the male alligators bellow very loudly. 
The eggs are laid sometimes in a hollow in the sand, and 
sometimes in a mound built by the reptile. The eggs are 
deposited in layers, with grass and sticks between. They 
are left to be hatched by the sun. Alligators seldom 
attain a length of twelve feet (Fig. 183). 

Characteristics of this order. — These reptiles are re- 
garded as the highest of the class, for several reasons. The 
heart, for example, is divided into four chambers which is 
much like that of the birds. The brain is more like that of 
the birds than the brains of other reptiles. The stomach 
is very birdlike. 

The crocodiles and alligators are covered with large, bony 
scales and the limbs are fitted for crawling and swimming, 
the toes being partly webbed. The jaws are furnished with 
many conical teeth implanted in sockets, and the eyes are 
well developed and furnished with three lids. 

Adaptations and habits of the reptiles. — Probably no 
group of vertebrates offers a more striking example of adap- 
tations to surroundings in the matter of coloring than 
snakes. There are the small grass snakes that are green 
in color to resemble the grass in which they live. Those 
snakes that live in trees are colored to resemble the bark 
or the leaves. There is a snake living in India that is per- 
fectly harmless, yet so closely resembles the hooded cobra 
in form, color, and markings that it deceives those well 
acquainted with both. The neck is dilatable like that of 
the cobra. There can hardly be a doubt that this is a case 
of protective resemblance. 



266 SNAKES, TURTLES, LIZARDS, CROCODILES 

Says Packard, " notwithstanding the fact that snakes 
have no legs, they can creep, glide, grasp, suspend them- 
selves, erect themselves, leap, dart, bound, swim, and dive." 
All of which shows that they are wonderfully well adapted 
to their environments. 

Many lizards possess feet adapted to climbing trees. 
The toes are long and end in claws especially well adapted 
to clinging to the bark of trees. The Old World chameleons 
have feet especially modified and adapted to clasping 
branches because they spend their lives in trees. The 
tongue of this lizard is remarkably well adapted to catching 
insects. 

More remarkable still, are the so-called flying dragons, 
or dracos of the East Indies. The dracos have a horizontal 
expansion of skin along each side of the body which is sup- 
ported by several of the posterior ribs. These animals, 
from seven to eight inches in length, live in trees and are 
constantly shooting through the air from tree to tree. by 
means of the side parachutes. Other lizards burrow in 
the ground and have their feet modified for digging. 

In considering the turtles, we find those that five in the 
sea have paddlelike legs for swimming, while those living 
partly on land and partly in the water have legs for walking, 
but the toes are webbed for swimming, while those wholly 
terrestrial have legs fitted for walking and toes without 
webs. 

The crocodiles and alligators are aquatic animals and 
possess at least one very remarkable adaptation for such 
a life. There is at the base of the tongue a transverse 
fold which, meeting a similar fold on the palate, completely 
shuts off the mouth from the throat, thus preventing the 
water entering the windpipe when they drown their prey. 



SNAKES, TURTLES, LIZARDS, CROCODILES 267 

The nostrils also have valves for closing them to keep out 
the water. The feet of the crocodile are webbed and the 
tails of both are flattened for swimming. 

CLASSIFICATION OF THE EXAMPLES 

Class — Reptilia. 

Order — Squamata. 

Suborder — Lacertilia. 
Types of Order. 

Cnemidophorus sex lineatus — Six-lined lizard. 
Eumeces quinquelineatus — Blue-tailed lizard. 
Sceloporus undulatus — Alligator lizard. 
Anolis carolinensis — American chameleon. 
Chameleo vulyaris — Old World chameleon. 
Phrynosoma cornutum — Horned toad. 
Heloderma suspectum — Gila monster. 
Suborder — Ophidia. 
Types of Order. 

Eutamia sirtalis — Garter snake. 
Python {several species) — Python. 
Naja tripudians — Hooded cobra. 
Agkistrodon contortrix — Copperhead. 
Agkistrodon mokasen — Water moccasin. 
Crotalus horridus — Rattlesnake. 
Order — Chelonia. 

Types of Order. 

Sphargis coriacea — Leather turtle. 
Chelone mydas — Green turtle. 
Chelone imbricata — Hawkbill turtle. 
Chelydra serpentina — Snapping turtlo. 
Chrysemys picta — Painted turtle. 
Trionyx spinifcr — Soft-shelled turtle. 
Testudo polyphemus — Gopher turtle. 
Order — Crocodilia. 

Types of Order. 

Crocodilus americanus — Crocodile. 
Alligator mississippiensis — Alligator 



XXII. BIRDS 

Chordata (continued) 

Class V. — Aves (am, bird) 

As a class, the birds are very uniform in their essential 
characteristics. There is probably not a bird in existence 
that would not be recognized as such on sight. The birds of 
the world have been grouped into nineteen different 
orders, seventeen of which are represented in North America. 
They are widely distributed and are of very great service to 
man, although their usefulness is poorly understood and 
but little appreciated. Notwithstanding the fact that all 
birds possess feathers, they exhibit a considerable variety 
of form and habits. Some are flightless and run upon land; 
some are flightless and live almost entirely in or upon the 
water; some have very great powers of flight and spend 
their lives flying over the sea, while others with equally 
strong wings soar high in the air over land. Some fish for 
a living, some come forth at night to kill, some scratch for 
their food, while others live upon seeds and various vege- 
table products. The study of birds with a field glass and 
camera, not with a gun, is one of the most interesting and 
enlightening lines of natural history work. 

Example of the Class — the English Sparrow 

Origin and distribution. — This sparrow was introduced 
into America from England about 1850 and for this reason 

268 



BIRDS 269 

it is called the English sparrow. It is not, by any means, 
confined to England on the Eastern continent, for it is really 
the house sparrow of Europe and Asia. This bird is now 
widely distributed over the United States and the southern 
portions of Canada. Throughout its range it is found 
principally in towns and villages or around farm buildings 
and along highways. It does not frequent mountainous or 
forested regions. 

External features. — We find the same general arrange- 
ment of the body parts as in the lizard ; namely, head, neck, 
trunk, and tail, the latter much shorter than that of the 
lizard. The limbs also differ markedly from those of the 
lizard or frog. The limbs of the sparrow may be designated 
as upper and lower, the former being modified into organs 
of flight while the latter serve as organs of locomotion on 
the ground and for perching. Over the whole body is a 
covering of feathers, the most characteristic feature of all 
birds. The anterior part of the sparrow's head is pro- 
longed into a bony structure known as the beak. The tail 
is furnished with long quill feathers. 

Plumage. — The body of the sparrow is not so uniformly 
covered with feathers as it appears to be. In some places 
the feathers are thin, in fact are entirely absent, while in 
others they are very numerous and thick ; but the thinner 
areas are covered over by the feathers overlapping each 
other so that no bare places are to be seen. There are four 
kinds of feathers on the body of the sparrow: the quill 
feathers, the contour feathers, the down feathers, and the 
thread feathers. The long feathers on the tail and wings 
are the quill feathers. The wing quills aid the sparrow in 
flying and the tail quills, acting together, serve both as a 
rudder and as a balancing apparatus when in the act of 



270 



BIRDS 




Fig. 184. 



Feather : a, quill ; b, rachis 
c, vanes. 



perching. All of those 
feathers that make up 
the general contour of 
the body and bear 
the color pattern are 
known as the contour 
feathers. They pro- 
tect the body from 
cold, rain, etc. They 
are efficient non-con- 
ductors of heat and 
retain the heat of 
the body. Lying be- 
neath and between 
the contour feathers 
are many small, soft, 
loose feathers that are 
known as the down 
feathers. They also 
serve admirably to 
retain the heat of the 
body. Finally, scat- 
tered over the body, 
but concealed by the 
other feathers , are cer- 
tain hairlike bodies 
known as the thread 
feathers. It is these 
that are left on a fowl 
after it is picked and 
that are removed by 
singeing. 



BIRDS 



271 



Amidst the feathers above the base of the tail is the oil 
gland which secretes an oily fluid that is distributed over 
the feathers with the beak. 

Structure of a feather. — A feather consists of two main 
parts, the quill and the vane (Fig. 184). The quill is a 
hollow, horny stalk, that extends from the origin of the 
feather to the vane. The vane is the flat, expanded portion 
of the feather. It has a longitudinal axis, the rachis, 
which is a continuation of the quill but differs in being 
solid. Running obliquely to the right and left, on each 
side from the rachis, are delicate, threadlike structures, 
called the barbs, which are closely held together by other 
delicate, threadlike structures running out from them, 
termed barbules. The latter are interlocked with one an- 
other, thus uniting the barbs and forming a continuous sheet. 
The feathers grow from small conical projections of the 
skin, called papillae. In this respect they differ from 
hairs which grow from deep invaginations of the skin. 

Wings. — Each wing consists of three parts : the arm, 
forearm, and hand (Fig. 185), which correspond with the 





,. J V Fingers 

Radius Handbones^ 



Humerus "' Ulna 

Fig. 185. — Bones of sparrow's wing. 



like parts of our own arm. The wings are concave on the 
inside and fit snugly to the body, really adding to the sym- 
metry and beauty of the bird. When the wing is folded, 
the arm, forearm, and hand form the letter Z, a position our 



272 



BIRDS 



'Jhigh 



arm cannot assume because our hand has not so much 
freedom of movement at the wrist. The long feathers that 
grow upon the end portion, or hand of the wing, are called 
the primaries and those on the forearm the secondaries. 

The wings are attached to the dorsal side of the body so 
that the weight of the latter will be suspended from the 
point of support when the bird is flying. 

Legs and feet. — The legs of the sparrow are slender and 
short, for they are not much used as organs of locomotion. 
Sparrows hop rather than walk and long 
legs are not needed. Like the wings, the 
legs are attached well toward the dorsal 
side of the animal so that the weight is 
suspended from the point of support. This 
f /Shank is of advantage to an animal that is obliged 
to reach the ground for all of its food. 
The hip joints act as pivots on which the 
body swings between the legs. 

Each leg consists of three parts : thigh, 

f^W- shank > and foot (Fig - 186 ^ The foot is 

made up of the four toes and the ankle 
Fig. 186.— Bones which is the scaly part of the leg not 
of sparrow's leg. cove red by feathers. Each toe is com- 
posed of several segments and ends with a claw. 

Perching. — The sparrow belongs to the perching birds. 
Whenever the feet of the sparrow are placed on a support 
and the body lowered, the toes will automatically close and 
grasp the perch. A tendon running from the toes passes 
up the leg in such a way that whenever the leg is bent, the 
tendon is pulled so strongly that the toes are curved about 
the support. The closer the body gets to the support, the 
more firmly will the toes grasp it. Therefore, the sounder 




\Foot 



BIRDS 273 

the sparrow sleeps, the more securely it sits upon its perch. 
In addition to this arrangement, there are muscles by 
which the bird can voluntarily cling to a support. 

The head and neck. — The head is small and light and 
the neck is long and muscular. Any animal that stands 
high from the ground must have a long neck with which to 
reach its food. At the same time the head must be as 
light as possible to enable such a long neck to support it 
without fatigue. The anterior part of the head is pro- 
longed into a hard, horny beak, the grasping organ of the 
sparrow. The beak consists of an upper and a lower man- 
dible, but is not furnished with teeth. No living bird has 
teeth. The beak is made to withstand the wear of picking 
food from the hard ground or other surface. Besides, it is 
used as a weapon of defense. 

The alimentary canal. — The gullet leads directly to a 
large pouch, the crop, in which the hastily procured food is 
stored for a time. The walls of the crop are provided with 
bands of muscles which, by their contractions, set up a slow 
churning movement. Following the crop is the slightly 
dilated and glandular stomach. Situated just a little be- 
yond and below the stomach is the thick-walled gizzard. 
The intestine immediately follows, forming, at first, a long 
loop, the duodenum, and then passing on toward the anal 
aperture, expands at its terminal part into a wide, saclike 
portion, the cloaca. Situated within the loop forming the 
duodenum is the pancreas which is directly connected with 
this part of the intestine. The gall bladder of the over- 
lying liver is also connected with the duodenum (Fig. 187). 

The digestive process. — The process of digestion is begun 
in the crop. Here the food is slowly churned and moistened 
by the juices given out by the glands of the crop. Passing 

herrick's zool. — 18 



274 



BIRDS 



on to the stomach the food is further acted on by the diges- 
tive juices of this organ. In the gizzard the food is masti- 
cated, as it were, and more thoroughly mixed with the 
digestive juices trickling into the gizzard from the stomach. 
In the absence of teeth, pebbles are swallowed and retained 



:Brain 




Intestine 
Pancfea§ 



Heart 
Liver 
-Breastbone 



Fig. 187. — Internal structure of a bird. 



in the gizzard to aid that organ in reducing the food. 
In the duodenum the food receives the final digestive 
ingredients, the bile from the liver and the pancreatic 
juice. 

The circulatory system. — The heart of the sparrow is 
four chambered and the left side is completely separated 
from the right side ; therefore there is a double circulation, 
that is, one set of blood vessels carrying impure (venous) 
blood and another set carrying pure (arterial) blood. 
Birds are very active animals, and the circulation is much 



BIRDS 275 

more rapid in them than in man, and the temperature of 
the blood is higher than in any other animals. 

Respiratory system of the sparrow. — In keeping with 
the active circulation of the blood, the respiration of the 
sparrow is also very rapid. The lungs are fastened to the 
dorsal walls of the body cavity and fit closely between the 
ribs. Connected with the lungs are certain large air sacs 
in the abdominal cavity. Moreover, many of the bones 
of the sparrow are hollow and contain air spaces connected 
with the lungs. 

Excretory system. — The main excretory organs are the 
kidneys, which are fitted into the spaces between the bones of 
the back in the posterior part of the body cavity. They are 
tri-lobed and discharge their excretions into the cloaca 
with which they are connected by slender ureters. 

Nervous system. — The brain is well developed and the 
anterior part consists of two large, smooth, pear-shaped 
bodies, the cerebral hemispheres, which constitute the cere- 
brum. The olfactory lobes project from the anterior ends 
of these hemispheres. Directly posterior to the cerebrum 
and on a middle line is the transversely furrowed cere- 
bellum. On the ventral side of the brain are the two optic 
lobes. From the brain the spinal cord runs throughout 
the length of the backbone, giving off nerves to all parts 
of the body. The nervous system of a bird is relatively 
large. 

Senses of the sparrow. — The nostrils of the sparrow are 
at the base of the upper mandible of the beak and open into 
the mouth. Yet we are not sure that a bird has a very keen 
sense of smell. On the other hand, we are positive that 
the sparrow has a well-developed sense of sight. This is 
true of all birds, especially of eagles and hawks. The eye 



276 BIRDS 

has three lids, an under and an upper lid and a third lid 
that can be drawn over the whole eye, known as the nictitat- 
ing membrane. The sparrow has no external ear, but the 
opening to the internal ear may be seen just back of and a 
little below the eye. It is covered by a tuft of loose feathers. 
The sense of hearing is keen, and birds depend upon their 
sense of sight and of hearing to detect their enemies. The 
sense of touch is distributed all over the body. 

Life history of the sparrow. — The sparrow builds its 
nest in almost any nook or cranny about the cornices of 
buildings or among the branches of trees. The nest is a 
simple one made of stems and twigs mixed with hair and 
grass and lined with feathers. Six to ten eggs are laid 
at a time and there are five or six broods in a season. 
Sparrows multiply very rapidly, and were it not for rats, 
mice, snakes, cats, etc., they would be much more abundant 
than they are. They are exceedingly hardy birds and crowd 
out other kinds. 

The sparrow's adaptation to flight. — In the first place, 
the general form of the body is conical, thus offering as 
little resistance to the air as possible. The covering of 
feathers give buoyancy to the body and aid greatly in sus- 
taining the weight of the animal in the air. The wings 
are placed near the dorsal side of the body so that the 
weight of the animal will hang suspended from the point 
of support and lessen the liability of being overturned in 
the air. The breastbone is furnished with a ridge, or keel, 
and the sides are long and sloping to afford space for the 
attachment of the powerful muscles that move the wings. 
Moreover, the large feathers on the wings and the manner 
in which they are arranged increase the surface of these 
organs of flight and enable them to present additional re- 



BIRDS 



277 



sistance to the air. The bones are filled with air spaces and 
there are large air sacs in the abdomen connected with the 
lungs, all of which tend to lessen the specific gravity of 
the body. 

Food and economic importance. — The food eaten by the 
English sparrow and the bearing this has upon its economic 
importance has been given considerable attention by the 
United States Department of Agriculture. In all, 632 
stomachs of these birds, of which 50 were nestlings, have 
been examined and the contents 
of each accurately determined. 
Figure 188 gives a graphic repre- 
sentation of the result of this 
investigation. Two per cent of 
the year's food consists of animal 
matter, chiefly insects ; 24 per cent 
of grass and weed seeds, and 74 
per cent of grain. The fact that 
grain was found to constitute FlG 188 
nearly three fourths of the food 
of the adult sparrows has brought 
merited condemnation upon this small but abundant bird. 
Moreover, the results of the examination of the 50 stomachs 
of nestlings bring additional reproach upon this sparrow. 
The food of the nestlings of our native sparrows, so far 
as we know, consists exclusively of animal food, mainly 
insects. In contrast with this it was found that 33 per 
cent of the food of the aforementioned 50 nestlings was 
composed of grain. In justice, however, it must be added 
that 65 per cent of the food consisted of insects, chiefly 
grasshoppers. Taking this record as a whole, we must 
class the English sparrow as decidedly injurious to agri- 




Diagram showing 
proportions of food of an 
English sparrow. 



278 BIRDS 

cultural interests. This bird does eat some weed seeds, 
especially in the public parks of cities and towns; but 
here again, the good it does is largely offset by the injury 
it works to buildings and statues, and we are driven to 
the conclusion that the bird is a serious pesc which ought 
to be exterminatedo 



XXIII. BIRDS (continued) 



Chordata (continued) 

Ostriches and cassowaries. — The ostriches and casso- 
waries are wholly unable to fly and are, therefore, known as 
the flightless land birds. At the same time, they are the 
lowest members of the class. The breastbones of these 
large birds differ decidedly from that of the sparrow, for 
they are flat, or unkeeled. 
This is in keeping with 
their small, functionless 
wings. The majority of 
these birds are large and 
possess strong legs with 
which they can kick 
viciously and effectively 
and run swiftly. 

The true ostriches live 
on the sandy plains of 
South Africa and Ara- 
bia. Unlike the spar- 
row, the feathers in the 
tail and wings of the 
ostriches are long and plumelike and furnish the feathers 
so commonly used for ornament. The ostrich is the largest 
living bird, measuring from six to seven feet in height. It 
has long, strong legs with two-toed feet and can run faster 
than a horse. Its wings are rudimentary and it does not 

279 




Fig. 189. — Cassowary. 



280 BIRDS 

fly. The male has black feathers on the body with white 
plumes on the wings and tail, while the female is of a 
sober, brownish gray. The eggs, which are five or six 
inches in diameter the long way, are laid by the female in 
a hole scraped out in the sand by the male. The male 
does most of the incubating. 

Ostriches are now reared on farms in Africa, South 
America, California, and Arizona. 

The so-called South American ostrich is not a true ostrich 
but belongs to a different genus from the one above. Its 
feathers are not so valuable, being used for rugs, dusters, etc. 

The cassowaries are large birds that, like the ostriches, 
have flat breastbones and rudimentary wings. They live 
in the dense forests of Australia, New Guinea, and other 
islands adjacent (Fig. 189). 

Loons, auks, and penguins. — These are all adapted to 
an aquatic life. They are expert divers and swimmers, 
and some of them are strong flyers. They are not at ease 
on land, because the legs are set far back, which gives them 
an awkward appearance, and ill adapts them to walking, 
but enables them to develop great propelling power in water. 
The feet are webbed. 

The common loon, often called the great northern diver, 
is migratory, ranging south to the Gulf in winter, but going 
north in spring, in pairs, to rear the young around some 
body of fresh water. The eggs are usually laid in rude 
nests among the reeds, close to the water. Loons have a 
peculiar loud call, hence the expression, "yelling like a loon.' 7 

The great auk was the only bird in North America in- 
capable of flight. It resembled the penguins in this re- 
spect, and nested on the islands in the North Atlantic. It 
is now extinct, having become so within the last generation. 



BIRDS 



281 



Penguins are preeminently aquatic birds and are found 
on the islands in the Antarctic Sea. The wings are small 
and adapted to swimming (Fig. 190), for they are used only 
as paddles. The legs are short and, on land, form very 
clumsy organs for walk- 
ing, but in the water 
serve as rudders. The 
penguins live in great 
flocks; and, in the egg- 
laying season, it is almost 
impossible to walk through 
the rookeries without step- 
ping on the young birds 
or eggs, so closely are 
they crowded together. 

Albatross and petrel. — 
These are representatives 
of a group of water birds 
that possess long, pointed 
wings and are strong, 
swift flyers. They are not 
water birds in the sense of swimming and diving, but 
rather in the sense of living near the water, flying over it 
much of their time, and eating fish and other animals 
found in water. 

The wandering albatross is a water bird of a very different 
type from the penguin. It is the largest water bird living 
and has the greatest wing expanse of any bird on the sea. 
The wings vary in different individuals from ten to twelve 
feet from tip to tip. It is probably the greatest flyer, in 
regard to distance and time spent on the wing, of any bird 
known. For days and days this bird will follow a vessel at 




Fig. 190. — Penguin. 



282 BIRDS 

sea, sometimes circling above it, sometimes just topping 
the furious waves, and sometimes skimming the calm sea, 
apparently ever on the wing. Some declare that it never 
rests at all in these long flights, but its feet are webbed, 
which is a pretty strong indication that it rests on the 
water at some time. 

There is a small, web-footed, sea -loving bird that is known 
to the sailors as " mother Cary's chicken." This is the little 
stormy petrel. It literally lives upon the sea, spending 
nearly all of its time in flying and skimming over the water 
just low enough to paddle the surface with the feet and 
assist the wings. * 

The gulls and terns. — The gulls are also strong and grace- 
ful flyers, but unlike the albatross and petrel they frequent 
inland bodies of fresh water, especially the Great Lakes 
and larger rivers as well as all the salt water bays and inlets 
of North America. The herring gull, which is our most 
common gull, wings its way far out to sea and also ranges 
far inland around the Great Lakes, the lakes and ponds of 
Michigan, Minnesota, and Iowa and the large rivers of the 
United States. 

The common tern, or "sea swallow," breeds in a few places 
along the Atlantic coast between New Jersey and Nova 
Scotia. It is much smaller than the herring gull and not 
so graceful, especially when it is on the ground. 

The cormorant and pelican. — These are water birds, and 
strong flyers like the petrels and gulls. The feet are webbed, 
the web even including the hind toe which is free in other 
birds. 

The cormorants are rapacious and greedy. They live 
and nest in great flocks, mostly along the rocky shores 
near the sea. Some of them, at least in former times, 



BIRDS 283 

nested inland. Their nests are loosely built of coarse reeds, 
seaweed, sticks, etc. They live largely on fish, and are of an 
iridescent, greenish black color, with green eyes a color 
not often seen in birds. They dive and swim with ease. 

The white pelican that occurs over much of the United 
States is a large white bird with long wings and webbed 
feet. It is remarkable for the large pouch beneath its bill, 
which is used for dipping up fish. One author says that 
" several thousand of them are permanent residents of Great 
Salt Lake, Utah, breeding on the islands twenty miles out 
in the lake." They make their nests on the ground and 
lay two to four eggs in it. 

Geese, ducks, etc. — The geese, ducks, and swans belong 
in the same group and are therefore closely related. These 
water birds have three toes of the feet webbed and their 
bills are rather broad and are furnished along each cutting 
edge with a series of toothlike processes. It is a large order 
and once each year its members come up from the tropics 
and subtropics to nest and rear their young. Some of 
them stop in the temperate zone, but many of them go be- 
yond the Arctic Circle among the lands of snow and ice. 

In. the autumn, after the young have waxed strong of 
muscle and wing, they retrace their long flight over land 
and sea to warmer regions to spend the winter. 

Of the ducks the mallard is the largest and handsomest. 
Besides, it is the parent of nearly all of our varieties of 
domestic ducks. It abounds in many parts of the United 
States, nesting in the tall grasses around the margins of 
ponds, beside small streams, etc. 

The canvasback duck has fallen a victim to the insati- 
able appetite of the epicure and is fast disappearing from 
North America. The eider duck occurs along the north 



284 BIRDS 

Atlantic coasts of Europe and America. The nests are 
lined with the soft down plucked by the female from her 
breast. This down, gathered from the nests, furnishes 
the eider down of commerce. 

The Canada goose is the common wild goose of America. 
It migrates in the autumn to the South in Y-shaped flocks, 
and returns North the following spring. It breeds in the 
northern United States and Canada. The nests, made of 
grass and sticks and lined with down and feathers, are 
usually placed on the ground. In most cases wild geese 
remain around lakes or rivers. 

Cranes, rails, etc. — The cranes are large birds with long 
legs and long necks. They frequent marshy places, ponds, 
rivers, and small streams. The whooping crane is white, 
with some black on each wing, and stands three to four feet 
high. The sandhill crane is common in the Mississippi 
Valley. The rails are smaller birds, with shorter necks and 
legs, and hardly any tail. Their legs are strong, and they 
depend on running, to a large extent, for safety. The 
Carolina crake is a small, slate-colored bird, much esteemed 
for food. 

Snipe and woodcock. — These are both highly prized 
game birds, with, perhaps, the woodcock higher in favor. 
Both of them have long, straight bills, with which they 
probe into the soft mud about the margins of ponds and 
streams in search of earthworms. The woodcock has a 
relatively large body, with short legs and tail, feeds mostly 
at night or in the shelter of undergrowth and is conse- 
quently difficult to kill. The snipe (Wilson's snipe) 
usually feeds in more open ground and when it takes flight, 
utters a shrill cry. 

Birds of prey. — The birds of prey include the eagles, 



BIRDS 



285 



hawks, owls, and buzzards. This group of birds is not a 
large one, but among its members are found both friends 
and enemies of man. The owls have been much maligned 
for their depredations upon poultry, but, as a whole, owls 
are among the most beneficial of all birds. There are 
eighteen species of owls in North America north of Mexico. 

The more familiar 

ones are the barn owl, 

the best feathered 

friend the farmer has, 

for it lives almost 

entirely on rats and 

mice ; the great horned 

owl, which it must 

be confessed destroys 

much poultry, yet, at 

the same time, kills 

many mice ; the 

screech owl (Fig. 191), 

and the long-eared 

owl. The burrowing 

owl is found on the 

plains of the West 

from North Dakota to southern California. This owl 

burrows readily into loose soil. 

The eagles (Fig. 192) are majestic birds of large size and 
furnish an inspiring spectacle in their lofty flights above the 
crags and mountain tops. The feet of the eagles are very 
strong and every toe is furnished with a strong, curved 
talon for grasping and holding the prey. The bill is short, 
stout, curved at the tip, and has sharp cutting edges. It 
is admirably adapted to cutting and tearing flesh, While 




Fig. 191. — Screech owl. 



286 



BIRDS 



eagles are on the wing, at 
a great height, they often 
locate their prey, and dash 
downward after it, for their 
sight is very keen. They 
live upon fish, birds, and 
mammals. Where food be- 
comes scarce, eagles carry 
away lambs and sometimes 
young pigs and fowls. 

Hawks are very similar 
to the eagles in all the 
points mentioned above 
and are closely related to 
them. See Fig. 193. 

The carrion crow and 
turkey buzzard that are so 
common in the South are 
Fig. 192.— Bald eagle. birds of prey also and be- 

long to the same order as the eagles and hawks. The 
buzzards live on dead animals and the claws are clumsy 
and not especially 
fitted for grasping. 

Quails, partridges, 
etc. — In this group 
of birds are found 
most of our domestic 
fowls; as hens, tur- 
keys, peacocks, etc. 

The quail, or bob- 
white, is perhaps the 
most noted game bird fig. 193. —Head of a hawk. 





BIRDS 287 

in this group. It ranges from Kansas, Indian Territory, 
and Texas to the Atlantic coast, and from the Gulf to 
Canada, They are usually founa in flocks called " coveys. " 
Their favorite nesting places are in the corners of fences, 
among the weeds in cultivated fields, and at the bases 
of stumps on the ground. The quail lays from twelve 
to twenty-five eggs. The ruffed grouse, or partridge, is 
common in the eastern United States. The male, standing 
on a log in the mating season, makes a well-known drum- 
ming sound by beating his body with his wings. Other 
birds belonging to this group are the ptarmigans, pheasants, 
prairie hens, etc. The bills of the members of this group 
are short and stout, and the feet, in most of them, are 
fitted for scratching. 

Doves and pigeons. — The doves and pigeons are rapid 
flyers. The toes, which are fitted for grasping and perch- 
ing, are usually on the same level. The base of the bill is 
covered by a soft membrane beneath which the nostrils 
open. They frequent cultivated ground in flocks in search 
of grains and seeds. The mourning or turtle dove is found 
all over temperate North America. 

Woodpeckers. — They have strong, sharp bills for drill- 
zing holes in wood. The tail feathers, which are stiff and 
sharp, aid in supporting the body of the bird when perched 
on the upright trunk of a tree. The feet have two toes 
pointing backward and two forward, an arrangement that 
also aids the bird in perching on a perpendicular surface. 
The red-headed woodpecker is abundant in the central 
United States. It excavates holes in trees, telegraph poles, 
etc., in which to build its nests. There are several species 
of woodpeckers in the United States. Some of them do 
much good by destroying the larvae of insects that bore 



288 



BIRDS 



into trees. These birds drill holes into the trees, impale 
the larvse on the long barbed tongues, draw them out, and 
devour them. The yellow-bellied sapsucker is a wood- 
pecker that is very 
fond of the sap of 
forest and fruit trees. 
And, although it 
devours many in- 
sects, it undoubtedly 
damages trees by 
boring rows of holes 
through the soft bark 
to obtain the sap. 

Whippoorwills, 
swifts, and humming 
birds. — This group 
of birds contains 
forms that differ 
so much from each 
other in appear- 
ances that their close 
relationship would 
scarcely be recog- 
nized. Their wings 
are long and pointed 
and, in general, they are swift flyers. With the exception 
of the humming birds, they live upon insects caught while 
the birds are in full flight. The whippoorwill is common in 
the eastern United States and is known by its peculiar call. 
In the daytime it remains silent and hidden in dark, deep 
recesses of the woods, coming forth only at night to 
chase insects. 




Fig. 194. 



Nest of a ruby-throated humming 
bird. 



BIRDS 



289 



The night hawk, or bull bat, is thought by some to be the 
same as the whippoorwill. It is a different species from 



Fig. 195. — Chimney swift. 

the whippoorwill, however. The night hawks are seen 
sailing and swooping through the air at dusk on summer 
evenings, in pursuit of insects. Strange to say, they make 




Fig. 196. —Nest of a chimney swift. 
herrick's zool. — 19 



290 



BIRDS 



hardly any nest, even depositing their eggs, at times, on 

bare rocks or on the roofs of houses, in cities. 
The humming birds are well known for their small size, 

long, slender bills, bright metallic colors, and the humming 

noise made by the rapid vibrations of their wings as they 

poise over a flower 
in search of nectar. 
Figure 194 shows 
the nest of the ruby- 
throated humming 
bird in the branches 
of an apple tree. 

The chimney swifts 
(Fig. 195) are seen in 
flocks passing down 
a chimney at night- 
fall. Here they build 
their nests of small 
branches glued to the 
sides of the chimney 
(Fig. 196). 

Parrots. — The par- 
rots are mainly in- 
habitants of the 
tropical parts of 
the world, especially 
South America and 




Fig. 197. — Carolina parrot. 



Australia. The bill is short and stout and the upper half 
extends beyond and curves over the lower half. The 
majority have a brilliant plumage, but some of them are 
dressed in sober hues. The tongue is large and soft and 
capable of very free movement. They are, by nature, great 



BIRDS 291 

mimics of the voices of other animals. The parrots vary 
in size, from the love bird, about the size of a sparrow, to 
the macaws, which often measure three feet from tip of bill 
to tip of tail. The only parrot found in the United States 
is the Carolina parrakeet. Formerly this parrot was found 
as far north as the Great Lakes, but now it is confined to 
Florida. It is very fond of cultivated grains and this has 
been one cause of its extermination (Fig. 197). 

The toes of parrots, like those of woodpeckers and cuckoos, 
are in pairs. One pair points backward and one pair forward. 

Perching birds. — This group of birds contains over six 
thousand species, more than all the others combined. 
Nearly all the familiar birds belong to the perchers. The 
crows, jays, orioles, robins, bobolinks, sparrows, mocking 
birds, thrushes, etc., are familiar examples. They are the 
most highly developed of all the birds, and stand at the 
head in complexity of organization. The feet of the perchers 
differ from those of the parrots in having one toe pointing 
backwards and three toes extending forward, thus enabling 
them to grasp the object on which they are resting. Many 
of them are very sweet singers. The mocking bird is con- 
sidered first in the range and variety of its notes. To the 
writer, however, the song of no bird will ever awaken so 
much joy or will linger so long in the memory as the notes 
of the Wilson's thrush heard lightly rolling and lingering 
through a wooded glen on a summer eve at twilight. In 
the mammals, the vocal cords by which sound is produced 
are situated at the upper end of the windpipe in the larynx. 
In the. singing birds a structure known as the " syrinx," 
or " lower larynx," is situated at the lower end of the wind- 
pipe, next to the lungs. It is here that the sounds are sup- 
posed to be produced. 



292 BIRDS 

Chief characteristics of the birds. — They are all covered 

with feathers. The queer "kiwi," or Apteryx, of New 
Zealand, possesses only hairlike feathers. No living birds 
possess teeth, but the jaws are modified into a beak incased 
in a horny covering. The heart is four chambered, and 
there is a consequent double circulation, — that is, one set 
of vessels carrying impure (venous) blood, and another set 
carrying pure (arterial) blood, which is like the circulation 
in man. The front pair of limbs is modified into organs of 
flight, which in some are nevertheless useless as such. The 
temperature of the body is higher than in any other animals. 
Therefore, for the first time we meet with warm-blooded 
animals. The bones of many birds are hollow and filled 
with air. Moreover, there are often air sacs in the body 
for the purpose of increasing the buoyancy of the animal. 

Molting of birds. — A feather does not continue, like a 
hair, to grow indefinitely; but after once attaining its 
growth, it remains unchanged until shed, when a new 
feather grows in its place. Generally speaking, birds shed 
all their feathers, or molt, once a year, after the breeding 
season is over. Some birds pass through two molts a year, 
one in the autumn and another in the spring. The feathers 
following the autumnal molt may be of one color, while 
those following the spring molt may be of another. Hence ( 
such birds possess a certain color in winter and another in 
summer, or, as we say, have seasonal colors. 

Incubation of birds. — All birds are developed from eggs 
laid by the female parent, usually in a nest of her own 
building. The time necessary for the incubation of the 
eggs varies with different birds. For the majority of birds 
the eggs are incubated from ten to thirty days, but an 
ostrich egg requires nearly fifty days of incubation. Some 



BIRDS 



293 



birds, for example the English sparrow, rear several broods 
of young a year, but most species have one or two. In 
some species the male aids in building the nest and takes his 
turn at sitting on the eggs, while in other species the 
female does practically all of the work of rearing the young. 
Nesting habits. — In building homes in which to deposit 
eggs and rear the young, birds differ greatly. Perhaps the 




Fig. 198. — Nest of a mocking bird. 



least careful birds in these matters are the auks. Some 
of these birds drop their eggs on the bare ground or among 
the loose stones and rocks with no attempt at making any 
nest whatever. The majority of birds, however, take great 
care in building their nests and concealing them from 
marauders. The Old World cuckoo and the cowbirds 



294 



BIRDS 



lay their eggs in other birds' nests, and allow the young to 
be fed and reared by foster parents. 

A kind of swift, found in the Polynesian Islands, builds 
its nests in caves, and constructs them of a mucous secretion 
which hardens into a tough gelatinous substance. These 
so-called " edible nests" are used as food by the Chinese. 




Fig. 199. — Oriole's nest. 



Many birds secrete mucus from the salivary glands which is 
used to fasten the materials together of which their nests 
are built. 

The hanging nests of our Baltimore orioles (Fig. 199) 
and of the japim of South America are objects of very 
great interest. The social weaver birds of South Africa 
build domelike structures out of straw beneath which may 
be twenty or thirty individual nests. The female hornbill 
of Africa, Asia, and Australia enters a hollow tree to build 



BIRDS 



295 



her nest. The entrance to the nest is then sealed up with 
mud by the male with the exception of a small hole through 
which the female presents her bill to be fed by her faithful 
consort. Finally, those wonderful little tailor birds of India 
select two or three leaves near each other and actually 




Fig. 200. — Nest of a blackbird. 



stitch the edges together, thus forming a neat receptacle 
in which to build their nest. 

But we do not need to travel to foreign countries to find 
interesting birds and nests. The habits and nest building 
of our own birds are always a source of wonderful interest 
and pleasure to those who study them. Figure 200 shows 
the nest of a blackbird. 

Migrations of birds. — A great majority of the birds that 
spend the summer in the colder portions of the earth go 



296 BIRDS 

southward as winter comes on. Most of the birds from the 
central and northern United States go to Mexico and Cen- 
tral America in the autumn, to remain during the winter, 
returning again in the spring. The extent of the migra- 
tions of different birds varies greatly. Some go to Alaska 
or the region of Hudson Bay to rear their young, returning 
in autumn to Mexico and the West Indies. Others go no 
farther than the Great Lakes, while others, known as 
resident birds, remain throughout the year in the same 
localities in which they are bred and reared. 

It is probable that the original cause of these migrations 
was a change in climate whereby there came about a 
scarcity of food. The birds were thus forced to journey 
to other regions in search of something to sustain life. 
The wandering, thus induced by force, has now been regu- 
larly practiced by so many generations that it has become 
a fixed habit, and probably these birds migrate now from 
instinct. 

In general, it may be said that the migratory birds go in 
spring to the region of their birth by a definite route. In 
fact, the routes of some birds have been carefully mapped 
out. The return in autumn is slower and the route is less 
definite. 

Adaptations to environments and mode of living. — In 
our discussions of birds many of the adaptations to their 
mode of living have been brought out, and many others 
are obvious, hence we only recapitulate them here. 

Of course, they are preeminently fitted for an aerial life. 
The fore limbs are modified into most ideal organs for flight. 
The breastbone in those birds that fly is of such a shape that 
it affords the most surface for the attachment of the great 
muscles that move the wings. The bones of many birds 



BIRDS 297 

are hollow, to give strength and lightness. Moreover, the 
hollow spaces are often connected by tubes with the res- 
piratory organs, by which means they may be filled with 
air, and the buoyancy thus increased. The wings are 
attached at the very highest part of the thorax so that the 
weight of the body is placed below the wings, when out- 
stretched. 

Note the penguins, in which the wings have been modi- 
fied into organs of locomotion in the water, while the ostrich, 
which lives en land and has no functional wings, is furnished 
with long, strong legs for running. 

The eagles and hawks have eyes and feet wonderfully 
adapted to their mode of living. The owls also possess 
eyes adapted to hunting in the night time, hence are able 
to avoid much competition in obtaining their food. 

We can hardly study the habits and structure of any bird 
without finding interesting adaptive modifications to its 
environment and mode of living. This phase of the sub- 
ject is a most entrancing and fruitful study. 

The extermination, protection, and economic value of birds. 
— The rapidity with whidi the birds are being extermi- 
nated is appalling to those who understand and appreciate 
their value to mankind. One of the mest striking instances 
of the tremendous decrease in the number of birds is 
shown in the case of the wild, or passenger pigeon. Alex- 
ander Wilson saw a flock of pigeons in Kentucky in 1808, 
that he estimated to contain 2,230,272,000 individuals. 
Great flocks of these pigeons continued common up to 1840, 
but now, not only the flocks but the individuals are becoming 
comparatively rare, especially in the northern United 
States. Birds are being lessened by hundreds by the fad for 
egg collecting, confined chiefly to boys. They are being 



298 BIRDS 

shamelessly killed by thousands to supply the demands of 
milliners. Birds are being destroyed by thousands in every 
state for food. Gun clubs, hunting contests, shooting boys, 
and cheap firearms are all enemies of birds. 

It is small wonder that the cankerworm, the palmer 
worm, the army worm, the curculios, the codling moth, the 
locusts and other insects are destroying three hundred 
million dollars' worth of farm and garden crops every year. 
It is a wonder that they do not destroy more. If this 
brutal, thoughtless, and indiscriminate warfare against the 
birds goes on much longer, we shall be wholly at the mercy 
of insect pests. 

Birds have both an aesthetic and an economic value. 
They are our best friends and our most cheerful companions. 
They always welcome us with a song. "When your ears 
are attuned to the music of birds, your world will be trans- 
formed. Birds' songs are the most eloquent of nature's 
voices; the gay carol of the grosbeak in the morning, the 
dreamy midday call of the pewee, the vesper hymn of the 
thrush, the clanging of geese in springtime, the farewell of 
the bluebird in the fall — how clearly each one expresses 
the sentiment of the hour or season." 

But since the aesthetic side of bird life is not always ap- 
preciated, let us consider the economic value of these ani- 
mals which depends upon their usefulness as destroyers of 
injurious insects, rodents, and the seeds of noxious weeds. 
In the air swifts are pursuing insects all day long and at night 
the whippoorwills and night hawks take up the quest. 
Flycatchers lie in wait for their prey and the light, active 
warblers skillfully pick insects from the leaves and blossoms 
of plants. The woodpeckers, nuthatches, and creepers 
explore the trunks of trees for hiding caterpillars and 



BIRDS 299 

grubs. The thrushes, sparrows, and other birds that live 
upon the ground devour myriads of insect foes. 

Let us consider some individual examples of the contents 
of birds' stomachs as a proof of their value as destroyers of 
insects, rodents, and the seeds of weeds. The stomach 
of one night hawk contained the remains of 38 grasshoppers, 
another 22, and still another 19. Nearly three fourths of 
the food of the meadow lark is composed of insects and over 
12 per cent consists of weed seeds. The stomach of one 
quail, or bobwhite, contained 101 potato beetles. Dr. A. K. 
Fisher examined 200 food pellets which had accumulated 
from two barn owls that roosted in a tower of a building in 
Washington and found 225 skulls of meadow mice, 179 of 
house mice, 20 of rats, 2 of pine mice, 6 of jumping mice, 
20 of shrews, 1 of the star-nosed mole, and 1 of the vesper 
sparrow. The stomach of one mourning dove contained 
7500 seeds of the yellow wood sorrel, while another con- 
tained 6400 seeds of barn grass. It is useless to multiply 
examples. If it were not for birds, the earth would be 
almost uninhabitable. 

CLASSIFICATION OF THE EXAMPLES 

Class — Aves. 

Division A — Ratitae. 
Order — Megistanes. 
Types of Order. 

Casuarius casuarius — Cassowary. 
Apteryx australis — Apteryx. 
Order — Rhese. 

Type of Order. 

Rhea rhea — South American ostrich. 
Order — Struthiones. 
Type of Order. 

Struthio camelus — Ostrich. 



300 BIRDS 

Division B — Carinatse. . 

Order — Impennes. 

Type of Order. 

Eudyptes antipodum — Penguin. 
Order — Pygopodes. 
Types of Order. 

Gavia imber — Loon. 
Podilymbus podiceps — Pied-bill grebe. 
Plautus impennis — Great auk. 
Order — Longipennes. 
Types of Order. 

Larus argentatus — Herring gull. 
Sterna hirundo — Common tern. 
Order — Tubinares. 
Types of Order. 

Diomedea exulans — Albatross. 
Procellaria pelagica — Stormy petrel. 
Order — Steganopodes. 
Types of Order. 

Phalacrocorax (several species) — Cormorants. 
Pelecanus erythrorhynchos — White pelican. 
Pelecanus fuscus — Brown pelican. 
Pelecanus californicus — California brown peli- 
can. 
Order — Anseres. 
Types of Order. 

Anas boschas — Mallard duck. 
Aythya vallisneria — Canvasback duck. 
Somateria mollissima borealis — Eider duck. 
Branta canadensis — Canada goose. 
Order — Paludicolse. 
Types of Order. 

Grus americana — Whooping crane. 
Grus mexicana — Sandhill crane. 
Porzana Carolina — Carolina crake. 
Order — Limicolae. 
Type of Order. 

Gallinago delicata — Wilson's snipe. 



BIRDS 301 

Order — Raptores. 
Types of Order. 

Halicetus leucocephalus — Bald eagle. 

Catharista urubu — Carrion crow. 

Cathartes aura — Turkey buzzard. 

Aluco pratincola — Barn owl. 
Order — Gallinse. 
Types of Order. 

Colinus virginianus — Bobwhite or quail. 

Bonasa umbellus — Partridge or ruffed grouse. 
Order — Columbse. 
Type of Order. 

Zenaidura macroura — Turtledove. 
Order — Pici. 

Types of Order. 

Melanerpes erythrocephalus — Red-headed woodpecker. 

Bucerus bicornus — Hornbill. 
Order — Macrochires. 
Types of Order. 

Antrostomus vociferus — Whippoorwill. 

Chordeiies virginianus — Bull bat. 

Chaitura pelagica — Chimney swift. 

Callocalia fuciphaga — Swiftlet. 

Trochilus colubris — Ruby-throated humming bird. 
Order — Psittaci. 
T} ,, pe of Order. 

Conurus caroiincnsis — Carolina parrot. 
Order — Passeres. 
Types of Order. 

Corvus braehyrhynehos — Crow. 

Cyanocitta cristata — Jay. 

Icterus galbula — Baltimore oriole. 

Dolichonyx oryzivorus — Bobolink. 

Passer domesticus — Sparrow. 

Mim us polyglottos — Mocking bird. 

Sutoria sutoria — Tailor bird. 

Planesticus migratoria — Robin. 

Hylocichla fuscescens — Wilson's thrush. 



XXIV. MAMMALS 

Chordata (continued) 

Class VI. — Mammalia (animals with milk glands) 

The mammals constitute the highest group of the animal 
kingdom. The class, Mammalia, includes animals of 
various forms and habits many of which are well known and 
are of very great service to man. Most of our domestic ani- 
mals belong to this class. 

An Example of the Class — the Gray Rabbit, or 
" Cottontail " 

External features. — The body of the rabbit presents four 
regions — head, neck, trunk, and tail, the latter being very 
short. The whole surface of the body, even the soles of the 
feet and the inside of the cheeks, is covered with soft hah> 
an epidermal structure characteristic of mammals. The 
rabbit has four legs, the hinder pair being much larger and 
longer than the front ones. Two long external ears and 
two prominent eyes are present on the head (Fig. 201). 

The covering of hair. — A hair is an epidermal outgrowth 
and arises from a deep cavity, or invagination of the skin. 
There are three kinds of hair on the rabbit. 

The short, soft, kinky hairs that form the greater part 
of the covering and constitute what we call the fur. 

The long, straight, black-tipped hairs that protrude 
through the fur. 

302 



MAMMALS 



303 



And the long, stiff, bristlelike hairs on the sides of the' 
upper Up and around the eyes. These last are tactile hairs 
and are situated deep in the skin in intimate connection 
with nerves. 

Eyes. — The eyes are set wide apart and the sense of 
sight is very keen. Each eye has two movable, opaque 
lids and an imperfect, vestigial nictitating membrane. 




Fig. 201. — Gray rabbit. 

Ears and nostrils. — The external ears of the rabbit are 
very long and large and can be turned in different directions 
to catch the sound. The inner ear is well developed and 
the sense of hearing is acute. This animal depends largely 
upon its sense of hearing to detect the presence of enemies. 
When hiding from danger in its form, its ears He flat along 
the body. At other times the rabbit rises up to its full 
height, pricks up its ears, and listens. 

The nostrils are longitudinal slits at the end of the nose. 



304 MAMMALS 

Evidently the rabbit's sense of smell is well developed for 
we often see it moving the end of the nose and upper lip 
as though in the act of sniffing. 

Mouth and teeth. — The mouth is bounded by soft lips 
and each jaw is furnished with teeth of two sorts, the in- 
cisors and molars. There are two pairs of long, curved in- 
cisors in the front of the mouth, one pair on the lower jaw 
and one pair on the upper. These have sharp, chisel-like 
edges which meet together and form a very efficient gnaw- 
ing apparatus. Just behind the large pair of incisors on 
the upper jaw is a second pair of small, scarcely noticeable 
incisors. The front surfaces of the incisors are covered 
with a very hard enamel, while the remaining portion of 
these teeth are of a softer material. Thus it happens that 
in gnawing the softer back portions are worn away leaving 
a sharp cutting edge of enamel in front. Moreover, these 
teeth grow as fast from their roots as they are worn off by 
gnawing. This is also true of the teeth of rats, mice, 
and other gnawers. The upper lip of the rabbit is split 
in the middle so as to expose the incisors and facilitate the 
work of gnawing. 

Back of the incisors there is a space on the jaws along 
which no teeth are found. In a clog's mouth, the canine 
teeth occupy some of this space. Finally, far back in the 
rabbit's mouth are the molars, or grinding teeth, six pairs 
above and five pairs below. The upper and lower molars 
meet by flat, corrugated surfaces. The lower jaw has a 
sliding, forward and backward movement, while chewing, 
thus grinding the food between the sliding surfaces of 
the two opposing molars. 

The food. — The rabbit is a vegetarian pure and simple. 
It lives upon clovers, grasses, buds and bark of trees, etc. 



MAMMALS 305 

The tongue. — The tongue of the rabbit is thick and 
muscular and attached to the posterior part of the mouth. 
It is flattened and tapered toward the front. The soft 
part of the tongue and certain areas on the thick part are 
furnished with taste buds. It is believed that the sense of 
taste is fairly well developed. 

The legs of the rabbit. — The fore and hind limbs, which 
are the organs of locomotion, differ considerably in size 
and strength. The hind legs are much longer than the front 
ones and are more muscular. The front legs are divided 
into upper arm, forearm, and hand. The upper arm is al- 
most hidden by the skin so closely is it applied to the side of 
the body. The hand has five digits, each ending in a horny 
claw. The hind legs are divided into thigh, shank, and 
foot, the latter having only four digits. 

Method of locomotion. — When quietly searching for food, 
the rabbit hops slowly about from place to place. When 

O O 

cO CD 

O CD 

Fig. 202. — Diagram to illustrate the tracks made by a rabbit running. 

frightened, it runs swiftly by long, powerful leaps performed 
with the strong hind legs. In leaping, the flexible body 
is bent nearly double, the long, hind legs are spread apart, 
and the hind feet are put clown last, ahead of the front ones 
and on the outside of the latter. The tracks made by a 
running rabbit are represented in Figure 202. The two 
tracks close together are made by the front feet, while the 

herrick's zool. — 20 



306 



MAMMALS 



two far apart and in front of the former are made by the 
hind feet. 

The digestive system of the rabbit. — The digestion of the 
food begins in the mouth where it receives the saliva from 
four pairs of salivary glands. The food then passes down 
the long gullet into the large stomach, at the lower end of 
which is a valve, the pylorus, which prevents food from leav- 
ing the stomach before it has been properly acted upon by 



Spinal cord 



y< Kidney 




Windpipe 
Gullet 
£ungs\ 

Heart 



Diaphragm 



Gall Madder Pancreas 



Urethm 
Bladder 



FiGo 203. — Internal structure of a rabbit. 



the digestive juices. Following the stomach is the small 
intestine, the first part of which is called the duodenum. 
The ducts from the gall bladder of the liver and from the 
pancreas enter the duodenum. The large intestine com- 
pletes the alimentary canal. At the junction of the small 
and large intestines is a large, long, blind sac, or pouch, the 
ccecum (Fig. 203). 

The body cavity of the rabbit. — The body cavity of the 
rabbit is divided by a partly muscular and partly tendinous 



MAMMALS 307 

partition, the diaphragm, into two complete cavities, the 
thorax and abdomen. In this respect the mammalia differ 
from all other living vertebrates. Usually the diaphragm 
lies transversely to the long axis of the body. In the rabbit, 
then, it lies vertically and in man it lies horizontally. 

The thorax, which is the anterior cavity, is bounded by 
the ribs and contains the lungs and heart. The abdomen 
is bounded by soft muscular walls and contains the liver, 
stomach, intestines, reproductive and excretory organs. 

Respiration of the rabbit. — On the floor of the pharynx, 
posterior to the tongue, is an opening, the glottis, that leads 
into the windpipe. The glottis is closed by a lidlike organ, 
the epiglottis, which prevents the food from falling into the 
windpipe. The larynx, or voice box, is situated at the 
upper end of the windpipe which divides into two branches 
before reaching the lungs. The lungs are lobed and filled 
with air sacs bounded by thin membranous tissues per- 
meated with capillaries. 

In taking in air the diaphragm is pulled backward by 
the contraction of its muscles and the walls of the thorax 
are expanded. These movements enlarge the thoracic 
cavity, which allows the air to rush into the lungs through 
the windpipe. An expiration is accomplished by the re- 
verse movements. 

Circulation. — The circulation of the rabbit is very 
similar to that of the sparrow. The heart is divided into 
two complete halves with the right auricle and right ven- 
tricle on one side and the left auricle and left ventricle on 
the other. 

The blood flows from the different parts of the body into 
the right auricle and thence into the right ventricle. From 
the latter it is sent through the pulmonary arteries to the 



308 



MAMMALS 



lungs to be purified. The blood is returned from the lungs 
through the pulmonary veins to the left auricle. From 

„ .„ . here it flows into the left 

Capillaries . . ' 

ventricle whence it is ex- 
pelled through a system 
of arteries to all parts of 
the body (Fig. 204). 

Excretory system. — The 
carbon dioxide and other 
waste materials gathered 
from the body by the 
blood is exchanged in the 
lungs for oxygen and ex- 
pelled through the wind- 
pipe. 

A pair of bean-shaped 
kidneys attached to the 
dorsal side of the abdo- 
men gather the nitroge- 
nous waste matters of the 
body and discharge them 
through the ureters into 
the urinary bladder. 

Brain and spinal cord. 

— The surface of the brain 

Capillaries ig not g^^y convoluted 

Fig. 204. — Circulation of a rabbit, show- V1 ,1 , c ,i i _ 

. +1 t +u , , , rp, A i like that ol the human 

ing the course of the blood. The dark 

vessels contain impure blood and the brain, thus indicating a 

light vessels pure blood. hw ^^ q£ intelligence# 

The brain consists of several distinct parts. In front is 
the cerebrum, made up of two large hemispheres, on the 
anterior extremities of which are the two club-shaped 




MAMMALS 309 

olfactory lobes. Posterior to the cerebrum is the cerebellum 
composed of one centrally placed lobe flanked by lateral 
ones. Beneath the cerebellum and posterior to it is the 
enlarged end of the spinal cord, the medulla oblongata. 
The spinal cord extends through its channel in the back- 
bone and gives off nerves to different parts of the body. I 

Reproduction and development. — The rabbit multiplies 
very rapidly. Several Utters, each containing five or six 
or even more individuals, are produced in a season, and were 
it not for the fact that so many of the offspring die, these 
animals would overrun this country. The young are born 
alive and are nourished by the mother rabbit for a time on 
milk secreted by the milk, or mammary glands. These glands 
producing milk for the nourishment of the young by the 
mother is characteristic of all mammals. 

Economic importance. — Rabbits often do serious injury 
to fruit trees by gnawing the bark from the trunks and 
girdling them, during the winter season when food is scarce. 
Occasionally, they injure gardens by eating the vegetables. 
Rabbits were introduced into Australia from Europe about 
1850 and in a few years had multiplied to such an extent 
that they became a most serious pest and the Australian 
government has spent large sums of money trying to get 
rid of them. In parts of California these mammals occur 
in great numbers and cause serious injury. 

On the other hand, the fur of the rabbit is used to make 
felt and nearly all of the " derby" hats are made from this 
material. The rabbit is also used for food to some extent 
in this country, especially by the negroes in the southern 
states. 

Habits of the rabbit. — This mammal ranges from New 
England and Minnesota to Yucatan and because of its 



310 MAMMALS 

abundance in all parts of this great area it is one of the 
most familiar of our wild mammals. It lives in fields over- 
grown with briers, among brush heaps, in wild plum 
thickets, along hedgerows, on the borders of woods, etc. 
Under ordinary conditions, a rabbit hollows out and 
smooths a place, called a "form," in some tuft of thick 
grass and passes its time here during the day. Its fur 
blends nicely with the dead or dying grass stems and the 
form furnishes a good hiding place. Sometimes rabbits 
enter burrows of other animals when hard pressed by their 
enemies, and occasionally they rest in hollow logs. In the 
winter they secure protection beneath brush piles and other 
shelters. 

They are exceedingly timid creatures and have no effec- 
tive organs of defense although they can scratch quite 
severely with their claws. They depend upon their senses 
of sight and hearing to detect their enemies and then upon 
their legs to escape. The color of the hair aids them in 
escaping observation 



XXV. MAMMALS (continued) 



Chord ata (continued) 
The Egg-laying Mammals (Monotremata) 

The order Monotremata includes those animals i> which 
the mammary glands are devoid of teats. Unlike all other 
mammals the members 
of this order deposit 
eggs, the duckbill two 
and the spiny ant-eater 
usually one. Moreover, 
a cloaca is present into 
which the ureters and 
urinary bladder enter 
separately. 

Duckbill. — Living in 
Australia and the ad- 
jacent island of Tas- 
mania is a curious and 
interesting animal 
known as the duckbill 
(Fig. 205). It is eight- 
een to twenty inches 
long, from the tip of its 
bill to the tip of its flat 
tail; and its body is covered with thick, dark brown fur 
except on the bill and feet. The feet have five toes fur- 
nished with strong claws, and the toes are webbed. The 

311 




Fig. 205. — Duckbill. 



312 MAMMALS 

webs of the front feet project beyond the claws, but can be 
folded back out of the way when the animal digs its bur- 
row. While young, the animal has four or five teeth on 
each jaw; but in the adult these are replaced by horny 
plates. 

The duckbill spends much of its time in the water, 
searching for grubs, worms, snails, and, most of all, mussels 
that live on the bottoms of streams. For a home, the ani- 
mal digs a burrow in the bank of some stream. The burrow, 
which has one opening above and one below the surface 
of the water, extends in a winding manner gradually up- 
ward, and finally ends in a large cavity made by the parent 
for the nest, which is several feet above the level of the water 
and, consequently, dry. The duckbill lays two or three 
true eggs, with soft, leathery shells. The young hatch from 
the eggs, and are fed by the milk secreted in the mammary, 
or milk, glands of the mother. Hence this animal is a true 
mammal like the horse or the cow. But unlike the cow, 
horse, and others, the milk glands of the duckbill and the 
following closely related animal, the spiny ant-eater, have 
no teats or nipples. 

Spiny ant-eater. — This animal is also found in Australia, 
but is smaller than the duckbill and differs markedly from 
the latter in habits and appearance. The ant-eater has 
its jaws produced into a narrow, bill-like structure and the 
upper surface of the body is covered with strong, pointed 
spines, between which are coarse hairs. The limbs are 
short and strong while every foot has five toes, each of 
which ends in a strong claw which enables the animal to 
burrow in the ground rapidly and efficiently. 



MAMMALS 313 

The Pouched Mammals (Marsupialia) 

The marsupials are divided into two orders (see p. 338) 
based on differences in the teeth. We shall treat them here 
as one group and give their general characters. 

The marsupials possess a pouch or fold of skin on the 
ventral side of the abdomen called the marsupium. The 
very short teats are on the walls of the abdomen inside of the 
marsupium. The young are born in a rudimentary condi- 
tion and are placed at once in the marsupium, where they 
cling to the teats and obtain nourishment. 

Kangaroos. — There are several species of kangaroos, 
all of which are found in Australia and the near-by islands 
of New Guinea and Tasmania. Most of these mammals are 
terrestrial and live in the " bush " or in open places, brows- 
ing on the grass and tender shrubs. A few species, known 
as the tree kangaroos, actually climb trees and live in them. 
The largest kangaroo is the great gray kangaroo, sometimes 
called " old man " and " boomer." The male, when in an 
erect position on its hind legs, often measures over four feet 
in height and weighs two hundred pounds. The animal is 
very timid, yet, when cornered, defends itself with spirit 
and effectiveness. When frightened it covers from fifteen 
to twenty feet in one leap, and can easily keep pace with a 
swift dog. The fore legs are short, and are folded close to 
the breast when running, all the leaping being done with 
the strong hind legs, aided by the long, massive tail. More- 
over, the tail acts as a balancing pole and enables the 
animal to maintain its proper position when in mid air. 

The smallest species are the rat kangaroos, some of which 
are only fourteen inches long. 

The milk glands of the kangaroo are situated within a 



314 



MAMMALS 



fold, or pouch of skin, the marsupium, on the ventral side 
of the abdomen. The young are born very immature, and 
are immediately placed by the mother in this bag, and are 
there carried for several months. 

Opossum. — As with the kangaroos, there are several 
species of opossums ; but the Virginia opossum, found from 

New York to Texas and 
south is the best known. 
The female has a pouch 
in which the young are 
carried for some months. 
They are only about one 
half inch long when born, 
and are immediately put 
in the pouch by the 
mother. This opossum 
is about the size of a cat 
and is dirty white in 
color. It has a long, 
naked tail, like a rat's 
tail, and lives largely in 
trees (Fig. 206). 

The marsupials are 
closely related to the egg-laying mammals, for, although 
they do not actually lay eggs, they come near doing so, as 
shown by the very immature young. 




Fig. 206. — Young opossum. 
ratlike tail. 



Note its 



The Toothless Mammals (Edentata) 

The edentates are mammals in which the teeth are absent 
or imperfectly developed in the adult. Sometimes molars 
and premolars are present, but they never form roots and do 



MAMMALS 



315 



not have enamel. The families of this order differ much 
among themselves from each other, for each family has its 
own peculiar characteristics. 

Sloths. — These animals well deserve their name, for, as 
Dr. Gill says, " They are not only slow to move, but slow to 
think, slow to feel, and slow to die." They are strictly 
arboreal, spending 
their lives among 
the branches of trees 
and very rarely com- 
ing to the ground. 
The natural position 
of a sloth is to hang 
suspended by the 
long, curved claws 
from a branch with 
the back downward. 
As some one has 
said, " He moves 
suspended from a branch, he rests suspended from it, and 
he sleeps suspended from it " (Fig. 207). They are often 
grayish in color, although some species are greenish, simu- 
lating very closely the leaves of the trees among which they 
live. The legs are comparatively long, especially the fore 
ones. When, for any reason, a sloth comes to the ground, 
it is exceedingly awkward, indeed almost helpless; for it 
can only walk with the greatest difficulty. They are found 
in the forests of South America, but some species come as 
far north as Nicaragua. The sloths are not large animals, 
for they range in size from a good-sized cat to a fox or 
raccoon. 

Armadillos. — Unlike the sloths, the armadillos are 




Fig. 207. 



Sloth sleeping suspended from a 
branch. 



316 MAMMALS 



burrowing animals, and, accordingly, are fitted with strong 

I claws for digging. The back and sides of the body are 

covered with a coat of mail composed of thick, overlapping, 
bony scales. In some species even the head, also, is 




Fig. 208. — Three-banded armadillo: at the left, walking; at the right, 
rolled up for protection. 

covered. This coat of mail is divided into three distinct 
portions, — an anterior portion covering the shoulders, a 
posterior portion covering the hips, and a middle portion, 
which is often divided into several distinct rings (Fig. 208). 
In the species shown, the middle portion is divided into 
three bands, hence this one is known as the three-banded 
armadillo. These breaks in the coating of scales afford 
flexibility, and give an opportunity for the animal to roll 
up into a ball, as it often does for protection (Fig. 208). 
In the three-banded armadillo, the head also is covered with 
scales, which afford fuller protection. There is only one 
species of armadillo in the United States, and that is 
confined to Texas. It is about two and one half feet in 
length, and lives in burrows. None of the armadillos are 
large animals, the largest being only about three feet long, 
exclusive of the tail. 



MAMMALS 



317 



The Fishlike Mammals (Cetacea) 

The whales, dolphins, and porpoises constitute the order, 
Cetacea. They are aquatic mammals with fishlike bodies. 
The fore limbs are paddlelike in form while the hind limbs are 
wanting. The snout is very long and there is a horizontal 
caudal fin and often a vertical dorsal fin. The teats are two 
in number and posterior in position. The skin is devoid of 
hair. 

Whales. — There are two distinct groups of whales, viz. 
those possessing strong functional teeth, — hence called 
the toothed whales; and those possessing no teeth in the 




Fig. 209. — Jaws of a whalebone whale, showing the baleen. 



adult stage, but having plates of " baleen " or " whale- 
bone " which take the place of teeth, — hence known as the 
whalebone whales (Fig. 209). The sperm whale, found 
largely in the southern Pacific, southern Atlantic, and 
Indian oceans, is an example of the toothed whales. The 
males are often sixty and seventy feet long. Between the 



318 MAMMALS 

skin and skull, on the right side of the massive head is a 
large cavity containing the substance known as spermaceti, 
formerly used to a great extent in the manufacture of 
candles. The nostrils open by a single aperture through 
the top of the head. This opening is the " blow hole " and 
from it issue the columns of vapor sent forth by the animal 
when respiring. These huge animals come to the surface, 
" spout " — send forth moisture-laden columns of vapor 
from the lungs — sixty to seventy times, then plunge below 
to remain from forty minutes to an hour and a quarter. 

There are several species of whalebone whales, but. the 
bowhead, or Greenland whale is best known for its oil and 
whalebone. It has no teeth, but the lower sides of the 
upper jaw are furnished with hundreds of parallel plates of 
baleen, or whalebone. These plates are fringed at the end 
and act very effectually as a strainer, to separate the small 
animals, upon which the whale feeds, from the water taken 
in with them. The right whales of the Arctic Seas, the 
razor-back whales, and the sulphur-bottom whales are 
the largest living mammals. The latter are often ninety 
to ninety-five feet in length. The whales possess mammae 
and suckle their young; but, superficially, they resemble 
fish more than mammals. The fore limbs are modified into 
paddles, while the hind limbs are wanting, and the body is 
incased in a thick layer of fat, the " blubber," which yields 
the oil so much sought after. 

Manatee and Dugong (Sirenia) 

These are also aquatic mammals with a fishlike body and 
only the forward, paddlelike limbs present. There is no 
vertical dorsal fin and the snout is not greatly elongated. The 



MAMMALS 319 

teats are two in number and anterior in position. The 
skin may bear scattering hairs. 

Manatee. — This curious mammal forms a sort of 
connecting link between the whales and the hoofed 
mammals. The American manatee occurs in Florida, 
Mexico, and Central America. It is found in certain 
rivers of Florida, and is protected from extermination 
by state laws. Its skin is smooth, but has scatter- 
ing hairs. It is nine to thirteen feet long and fre- 
quents the mouths of rivers. The molar teeth have flat 
crowns for grinding vegetation, for the manatee lives upon 
aquatic plants. The fore limbs are modified into paddles and 
the rounded, thin, flat tail acts as a propelling organ, while 
the hind limbs are wanting. The flesh of a closely related 
species is used for food by the South American natives. 

There are certain sea cows, known as dugongs, found 
along the eastern coast of Africa and the coasts of India, 
Ceylon, and Australia. 

The Hoofed Mammals ( Ungulata) 

The hoofed mammals are chiefly herbivorous and the skin 
may bear an abundant covering of hair or the fur may be 
scanty. The claws or nails of other mammals are replaced 
by a horny hoof which bears the weight of the body, and the 
canine teeth are absent. 

The hoofed mammals may be divided into three groups: 
those that possess an odd number of toes, the horse, zebra, 
ass, tapir, and rhinoceros; those with an even number of 
toes, giraffe, camel, deer, oxen, hog, and hippopotamus; 
and a third group including those that have a trunk, or 
proboscis, represented by the elephant. 



320 MAMMALS 

It is a curious and interesting fact that the hoofed mam- 
mals walk on the ends of their toes, which, however, are 
incased in a horny covering called a hoof. The hoof is a 
modification of the skin. 

Among the odd-toed mammals are the tapirs that live 
in the tropical forest regions of both continents. They 
resemble hogs in appearance and form, but have a large, 
prehensile upper lip. 

The rhinoceroses, which have three toes on each foot, are 
found in Africa and Asia. They have a very thick skin 
which, in some species, is thrown into folds. The snout 
bears one or two horns quite different in structure and origin 
from those of cattle. The Indian rhinoceros has one horn ; 
while the black rhinoceros of Africa has two, one situated 
in a line directly behind the other. The white rhinoceros 
of Africa is a huge beast rivaled in size among the land 
animals by the elephant only. 

The horse has only one toe, but the so-called " splint 
bones " are the existing remnants of a second and a fourth 
toe. In the western states a remarkable series of fossils 
have been found showing the development of the horse 
from forms about the size of a fox with three toes behind 
and four toes in front. 

The even-toed group of hoofed mammals have as their 
lowest representative the hippopotamus, of which there 
are only two species, both found in Africa. They have 
four toes, a huge, ungainly body, and large canine teeth 
developed into tusks. They may be seen in large herds in 
the rivers of Africa, in the daytime, apparently for the 
simple pleasure of being in the water. They can remain 
beneath the water for a considerable interval of time, and 
to facilitate such a habit the nostrils can be closed by 



MAMMALS 



321 



muscular contractions. They live on aquatic plants and 
the herbage along rivers. 

Certain species of the even-toed mammals differ from the 
hippopotamus in the structure of the stomach and in the 
manner of masticating the food. For example, an ox, 
sheep, camel, deer, etc., are said to " chew the cud." 
Therefore, these mammals are known as ruminants. 




Fig. 210. — Stomach of a ruminant: a, gullet; b, rumen; c, reticulum; 
d, psalterium; e, abomasum. 

The stomach of a ruminant is divided into four compart- 
ments, known, respectively, as the rumen, or paunch ; the 
reticulum, or honeycomb; the psalterium, or book ; and the 
abomasum, or stomach proper (Fig. 210). While an ox is 
grazing, the food is swallowed without mastication, and, 
together with saliva, passed directly into the rumen, or 
paunch, and reticulum. After the animal finishes eating, 
the food is brought back to the mouth — a small quantity 
at a time, which constitutes the cud — and is thoroughly 
masticated. This time, after being swallowed, the food 
goes to the psalterium, and thence to the abomasum, or 

herrick's zool. — 21 



322 MAMMALS 

fourth stomach, where the gastric juice is mixed with it. 
To the ruminants belong most of our valuable domesti- 
cated animals. 

Although the camel is a ruminant, its stomach has only 
three compartments, the psalterium not being present. 
The dromedary has one hump and its body is covered 
with a fine wool hair, except on the breast and knees, the 
latter being covered with thick pads of skin. This is the 
beast of burden used in traveling across the deserts of 
Africa and Arabia. It is expected to go from three to five 
days without water during these journeys, but ordinarily 
demands water every other day. On the under side of 
each of its feet is a large spongy pad which enables the 
animal to travel over the sand with comparative ease. The 
camel inhabiting central Asia has two humps. 

The llamas and alpacas, found in the western parts of 
South America, are members of the camel family. The 
llama is still used as a beast of burden, while the alpacas 
are reared for their wool which is used in the manufacture 
of dress fabrics. 

The third group of ungulates is represented by the ele- 
phants. There are only two representatives of living ele- 
phants, the African and the Asiatic. The former is wild, 
and valued for the ivory of its tusks. The latter is domes- 
ticated and is usually docile and intelligent. The head of 
the elephant is very large, and would be almost insupport- 
able from its enormous weight were it not for the fact that 
the bones of the head contain cells filled with air. 

The upper incisor teeth are greatly developed and form 
the tusks. The neck is very short, but the snout is pro- 
longed into a long flexible trunk, or proboscis. At the end 
of the trunk are the openings of the nostrils, which are 



MAMMALS 



323 



overarched by a small fingerlike process. The trunk is 
a wonderfully mobile and versatile organ. In it Cuvier 
counted twenty thousand muscles, became discouraged, 
but estimated the number to be forty thousand. With it 
the elephant can lift a cannon or pick up a lozenge or 
brush off a fly or uproot a tree. 

Flesh-eating Mammals (Ferce or Carnivora) 

The mammals of 
the order, Carnivora, 
are flesh-eating 
hence the canines 
and molars are well 
developed. The skin 
is well covered with 
hair and all the 
digits are provided 
with claws which, in 
many cases, are re- 
tractile. 

If we have 
observed closely, 
we have seen that 
the hoofed mam- 
mals were distinctly 
plant-eating, or 
herbivorous ani- 
mals. We now 
come to a group of 
animals that are 
distinctly flesh-eat- 
ing, or, as they are 




Fig. 211. — Raccoon. 



324 MAMMALS 

called, carnivorous. The teeth are fitted for cutting or tear- 
ing rather than for grinding, and the stomach is single. 

The flesh-eating mammals are represented by the rac- 
coon, bear, lion, tiger, dog, cat, wolf, fur seals, etc. 

. The raccoon is widely distributed over the United States 
and is commonly known by the simple appellation of 
" coon " (Fig. 211). It will eat almost anything from 







Fig. 212. — Lion in the act of springing. Redrawn, by permission, from 
an illustration by Knight in McClure's Magazine, 1900. 

green corn to oysters. The body is clothed with thick gray 
fur mixed with black, and the tail is long, large, and cylin- 
drical, and ringed with gray and dark brown. 

The black bear, which is found over the greater part of 
the United States, is known as a " plantigrade " animal 
because it walks on the whole sole of its foot. Like the 
coon, it is somewhat of a vegetarian and is fond of berries, 
acorns, and nuts as well as of lambs, pigs, and calves. 
Generally speaking, it hibernates during the winter. 



MAMMALS 325 

The grizzly bear, which lives among the Rockies, is the 
most ferocious and largest of the bears. It often weighs 
six to eight hundred pounds. 

The lion (Fig. 212) is simply an enormous cat ; it is some- 
times called " king of beasts." The light, springy, silent 
step and graceful, almost majestic stride of the lion differ 
markedly from the clumsy, heavy step of the bear: A 
lion may attain a weight of six hundred pounds. 

The tiger is a beautiful and magnificent cat found in 
southern Asia from Persia to India, and in the Malay 
Peninsula and the adjoining islands of Sumatra and Java. 
It equals and, it is said, exceeds the lion in size; without 
question, it exceeds the lion in strength and ferocity. 

The fur seals, walruses, etc., are flesh-eating mammals 
that have limbs greatly modified and fitted for swimming. 

The fur seal. — Really, the fur seal (Fig. 213) belongs to 
the family of sea lions. The true seals have short necks and 
fat bodies, while the sea 
lions have longer necks and 
are much more active in the 
water and on land. 

The fur seal is very in- 
teresting because of its 
habits and economic value. CS BBM I m VJJl? ' "~~ 
The full-grown male seal ^: 7~ -~^~ 

weighs from four hundred _ 

& Fig. 213. — Fur seal 

to five hundred pounds; 

but the female is much smaller, often not weighing over one 
hundred pounds. The legs of this mammal are flat and wide, 
and the toes are united to form paddles for swimming, 
although the hind limbs serve to scramble about over the 
rocky beaches. 




326 



MAMMALS 



Once a year all the seals, young and old, repair to the 
Pribilof Islands in the Behring Sea. The males arrive first 
in April and May, and in June the females begin to come. 
Certain suitable rocky shores of these islands that are 
literally covered with the seals are known as the " rook- 
eries." In 1870 there were estimated to be several million 
seals on the Pribilof Islands, but the number is rapidly 
diminishing. The bachelor seals, or " holluschickie," 
are the only ones now allowed to be slain, and it is these 
that furnish the skins for the market. 

By October and November, the great majority of the 
seals have left the islands, not to return until the following 
spring. The time between the visits is spent in the open 
ocean, the seals seldom, if ever, touching land in all this 
time. 

Walruses. — These are aquatic mammals of strange ap- 
pearance and peculiar habits (Fig. 214). A male walrus is 




Fig. 214. — Walrus. 

a huge beast, ten to twelve feet long and weighing from 
eighteen hundred to two thousand pounds. The canine 
teeth are developed into huge tusks sometimes two feet 



MAMMALS 327 

in length. These animals are active in the water, but 
on land they are well-nigh helpless and can be easily 
approached and killed. They inhabit the northern At- 
lantic and Pacific oceans and are of great use to the natives 
around Behring Strait. The flesh is used for food, the skins 
for roofs of houses, for dog harnesses, and for fishing lines. 
The tusks are used for making implements and are sold in 
trade. 

The Gnawing Mammals (Rodentia) 

The members of this order of mammals are usually small in 
size and possess a furry (sometimes spiny) covering. The 
canine teeth are absent, but the incisors are long, with chisel- 
like edges and grow from the roots as fast as they are worn 
down by gnawing. 

Technically, these animals are known as the Rodentia, or 
rodents, — both words being derived from the verb rodo, 
gnaw. In this group are included the rat, mouse, rabbit, 
woodchuck, squirrels, etc. 

The teeth of the rabbit have already been described and 
their fitness for gnawing has been explained. The rat, 
which, perhaps, is a more typical gnawer, has only two in- 
cisors on the upper jaw, but they meet the incisors on the 
lower jaw in the same manner as do those of the rabbit and 
are kept sharp in the same way. Keeping, then, the general 
form and peculiarities of a rodent's teeth in mind, as exem- 
plified by those of a rat and rabbit, we shall pass to others 
of the group. 

Porcupines. — These animals are also gnawers, and the 
species found in the United States are more or less aboreal 
(Fig. 215). The Old World porcupines are strictly ter- 
restrial. Porcupines are covered with coarse hairs among 



328 



MAMMALS 



which are the spines, or quills, which constitute a notably 
efficient means of defense. When on the defensive, a por- 
cupine arches its back and rolls up into a ball. The tail, 

which is thickly 
covered with spines, 
is the main organ of 
defense. The un- 
wary dog or person 
worrying the porcu- 
pine is often caught 
within striking dis- 
tance. The spines 
are rough and 
jagged at the ends, 
but sharp, and when 
they once enter the 
flesh, tend to work 
farther in. 

Prairie marmots. 
— These little ani- 
mals, better known 
as " prairie dogs," 
are closely related to 
the woodchuck of 
New. England and the middle states. The best-known 
species is found on the prairies west of the Mississippi 
River. They live in colonies and dig deep burrows in the 
ground. The great quantities of earth brought up in dig- 
ging these holes are piled in a mound near the mouth of the 
burrow. 

Beavers. - — The beaver is one of the largest and heaviest 
rodents, often weighing thirty to fifty pounds. The body 




Fig. 215. — Porcupine in tree top. Redrawn 
from an illustration by Dugmore in McClure's 
Magazine, 1900. 



MAMMALS 329 

is covered with a thick coat of soft fur beneath a layer of 
longer coarse hair. The hind feet are webbed for swimming, 
but the fore feet are fitted for digging. 

Moreover, the beaver is one of the greatest gnawers of 
the whole group. It lives in colonies and is very indus- 
trious ; but most of its work is done at night. The houses, 
or " lodges," of the beaver are built on the edge of the water, 
are dome-shaped, and some four or five feet high. They 
are built of stones, sticks, and mud, and are finally plastered 
over in the autumn with mud, which freezes, thus forming a 
hard impenetrable shell. The opening into the lodge is 
beneath the water. The living apartment is at the top, 
above the water line; but near by are stored branches of 
,trees, the bark of which serves for the winter food. In 
order to maintain the water at the desired height about 
their lodges, the beavers build dams of considerable length 
(perhaps the longest ever noted being three hundred yards) 
across streams, with the convex side upstream, to with- 
stand the pressure. The dam is built of sticks, stones, and 
mud, not in regular fashion, yet forming a water-tight and 
very firm barrier. 

Insect-eating Mammals (Insectivora) 

The order, Insectivora, contains only very small mammals 
with a thick, furry (sometimes spiny), covering. The muzzle 
is short and soft and the molars are fitted for crushing the 
bodies of insects. They live mostly on insects and the order' 
includes the shrew, moles, hedgehogs, and some other little- 
known mammals. 

Shrews. — These are the smallest of mammals. One 
species known as the least shrew, which measures only a 



330 MAMMALS 

trifle over two inches in length, is surely quite a contrast 
with those other two gigantic mammals, the elephant and 
the whale. The shrews greatly resemble small mice. The 
body is covered with a coat of soft, furry hair ; but the eyes 
are small and often hidden in the fur, for these animals 
burrow beneath the surface of the soil and are not often 
seen by day. They live largely in the woods, and some 
species are aquatic. 

Moles. — Probably the moles are the best-known mam- 
mals of the insectivorous group. They are often held 
responsible for serious injury when, in reality, they do more 
good than harm. 

The shoulders and fore legs of the mole are very short 
and stout ; and the fore feet are broad and shovel-like, with 
each toe ending in a strong, sharp claw. Thus the animal 
is fitted for digging. The nose is long and slender, and the 
body is covered with a very fine, soft, dense coat of hair. 
Since the mole lives in the earth, it has no need for well- 
developed eyes. In fact, the eyes are situated beneath the 
skin and serve only to distinguish daylight from darkness. 

Like the shrews, the mole lives on earthworms, insects, 
and the larvae of insects, or " grubs," that exist in the soil. 
To obtain these, it becomes necessary to burrow here and 
there through the soil. Hence the burrows made by the 
mole are dug in quest of worms and " grubs,' 7 and not oi 
seeds or roots. 

The hedgehog is an Old World mammal belonging to the 
Insectivora. It has spines on its body, and when attacked, 
rolls up into a ball like the porcupine. The largest may 
slightly exceed a large rat in size. The term hedgehog 
is often applied to the porcupine, which we have already 
studied in the group of gnawing mammals. 



MAMMALS 331 

Winged Mammals (Chiroptera) 

The winged mammals have the anterior pair of limbs very 
greatly modified to form organs of flight. The bones of the 
fingers and hand are greatly elongated and covered with a 
broad, leathery membrane. 

There are nearly four hundred and fifty species of this 
order of mammals and they are found in various parts of 
the world. The bats vary in size and appearance. The 
largest species are found in tropical countries. 

Common bats. — The best-known members of this order- 
are the small or medium sized bats so common everywhere 
in the United States (Fig. 216). Perhaps the little red bat 



Fig. 210. — Rat. 

and the small brown bat are the most common species. The 
fore limbs which constitute the wings, or organs of flight, 
have the bones of the fingers and hand greatly elongated, 
spread far apart, and covered by a leathery membrane, 
which extends along the sides of the body to the hind legs. 
Only four of the fingers are included in the wing. The 



332 MAMMALS 

fifth is free and forms a sort of hook, or claw (Fig. 230). 
The membrane covering the fingers and forming the wing 
is nearly or quite devoid of hair. The bodies of bats are so 
much like those of mice, in general, that the Germans call 
them " flitting mice." The eyes are small, but the ears are 
large, and the sense of touch is acute. The hind legs are 
small and weak. 

The common bats are nocturnal in habits. During the 
day they remain hidden in a hollow tree, cave, or dark 
recess, coming forth to seek their prey at twilight and night. 
Those bats that live in cold climates and do not migrate, 
hibernate during the winter. 

The fruit-eating bats found in India, Ceylon, the Malay 
Archipelago, and eastern Australia are of large size and 
have foxlike heads with large eyes and are diurnal in 
habits. They feed almost exclusively upon fruits. The 
fruit bats or flying foxes of Ceylon often have a wing ex- 
panse of forty inches. They frequently live in colonies of 
fifty or more individuals. 

In the valleys of the Amazon and in other parts of South 
America are found the true vampire bats. These actually 
suck the blood of wild animals and in some localities cause 
considerable injury to domestic animals. Moreover, the 
vampires often bite human beings on the nose or feet while 
asleep at night. These bats are all small, their bodies 
measuring less than four inches in length. 

The First Mammals (Primates) 

The Primates are characterized by having prehensile 
limbs because the pollex, or thumb and the hallux, or great toe 
are opposable to the other digits. There are usually five 



MAMMALS 333 

digits in both hand and foot and each digit is furnished with 
a flat nail. The orbit of the eye is surrounded by a complete 
bony rim. 

We have finally reached the highest group of mammals 
and, at the same time, the highest group of animals in the 
kingdom. They are, therefore, known as the Primates. 
The primates include the lemurs, monkeys, baboons, 
( chimpanzee, orang-outang, gorilla, gibbon, and man. 

The lemurs are apelike mammals living in India, tropical 
parts of Africa, and the Island of Madagascar. They are 
the lowest members of the Primates. The baboons are 
found in Arabia and Africa and usually live in troops, often 
raiding plantations at night. They are fond of berries, 
tamarinds, and other fruits, but usually destroy and carry 
away more of these fruits than they eat. They are repul- 
sive animals and their faces resemble that of a dog, while 
they can walk easily and handily on all fours. 

The orang-outang is one of the four primates that stand 
nearest to man, the other three being the gibbon, chim- 
panzee, and gorilla. The orang-outang is found in the low 
swampy parts of the Island of Borneo and rarely in Sumatra. 
It is about four feet six inches high, is strictly arboreal, 
and travels by swinging from branch to branch. It con- 
structs a rude nest in trees some twenty or thirty feet from 
the ground. 

The chimpanzee, in general appearance,, is more like man 
than any other of the tailless apes. It is found in central 
and western Africa and even north to the Sudan. The 
body is more or less covered with a coat of shiny, thick 
hair, very dark, nearly black in color. It is a good climber 
and makes its nest of sticks and broken limbs in the forks 
of branches of trees ten or twenty feet above the ground. 



334 MAMMALS 

The gorilla is the largest of the manlike apes, often reach- 
ing a height of five feet, four or six inches. It lives in deep 
forests, in a very restricted portion of western Africa in the 
Congo district. Its forehead retreats strongly, its expres- 
sion is brutal, and the body is more uniformly covered with 
hair than that of the chimpanzee. The gorilla naturally 
walks on all fours, but it can walk erect although rather 
clumsily. Its ferocity has been exaggerated. 

Man. — As an animal, man belongs to the family Homin- 
ida? and is known scientifically as Homo sapiens. As an 
animal, he is distinguished for his erect posture, very com- 
plete opposition of the thumb to the fingers, short canine 
teeth, greater length of hind, as compared with fore limbs, 
and the great size and complexity of the brain. 

Characteristics of the mammals. — As we have already 
learned, the name of the class is derived from the fact that 
the young are nourished for a longer or shorter time on milk, 
which is a fluid secretion from certain specialized glands 
known as mammae. Secondly, it may be said that the 
bodies of mammals, at some period of their existence, are 
more or less covered with hair. We have seen from our own 
study and observation that many are completely covered 
with hair, except the nose and soles of the feet. On the 
other hand, the whales are wholly destitute of hair, or very 
sparsely clothed with it, in the adult stage ; but it is present 
on portions of the body in embryonic whales. Moreover, 
the heart, as in birds, consists of four chambers, the two 
on one side being completely separated from the two on the 
other side. Hence, there is a double circulation. The 
thorax is separated from the abdomen by a strong muscular 
partition known as the diaphragm. This aids greatly in 
respiration. The mammals, in general, bring forth their 



MAMMALS 335 

young alive. We found exceptions in the duckbill and 
the spiny ant-eater, both of which lay eggs. 

Upward progression among the mammals. — The duck- 
bill, the lowest mammal, ushers in the class. Superficially, 
this animal resembles a bird so that one might think the 
Mammalia more closely related to the Aves than to any 
other class among the vertebrates. Modern zoologists are, 
however, inclined to think the mammals had for an ancestor 
some animal of very strong reptilian characters, because 
the duckbill and spiny ant-eater possess reptilelike charac- 
ters. Whatever kind of an ancestor mammals had, they 
show a great advance over any other group of animals in 
complexity of structure. A most important advance among 
the mammals themselves is a constant tendency for the 
body to develop head ward. The brain becomes larger 
and larger, and the fore limbs become modified into hands 
for grasping, exemplified in man. Moreover, there is a 
development among the mammals toward an upright 
position, again exemplified in man. This " holding up of 
the head " seems to go along with the increase in size of 
brain. The complexity of the teeth and the structure of 
the limbs show a decided step in advance over the birds and 
reptiles. 

Adaptations to environments among the mammals. — 
Whatever forces compelled the duckbill to live the life it 
does, other forces just as surely molded and adapted it to 
that life. Its food is found mainly under water, and to 
obtain this food, the duckbill is obliged to remain sub- 
merged some time. Consequently, although a terrestrial 
animal, it has become adapted to staying beneath the water 
some six or seven minutes at a time. Its feet are webbed 
for swimming, yet the web on the front pair can be turned 



336 MAMMALS 

back out of the way, thus exposing the claws so necessary 
for digging its burrows. The spiny ant-eater is furnished 
with strong claws for tearing open the ants' nests. In 
addition, it has a long, sticky, extensile tongue with which 
it can lick up the ants by the hundred and thus obtain a 
meal. 

The sloth passes its existence in trees. Yet how curiously 
adapted to such a life it is. What wonderful muscles it 
must have never to weary of hanging down, either in its 
waking or sleeping moments. Try the experiment of hold- 
ing your own weight by suspending yourself from a bar, 
by your arms, for five minutes. It will give an idea of 
what the sloth's mode of life means to its muscles. Note 
that the claws are also modified for grasping the branches. 
Many sloths possess hair resembling leaves in color, thus 
affording them protection. I suspect they were driven to 
such a mode of living partly for the sake of protection. The 
armadillo, however, which belongs to the same order, in- 
stead of climbing trees took upon himself a coat of armor, 
so flexible that he can roll up inside of it for protection. 

Perhaps among mammals the most remarkable modi- 
fications and adaptations are found among the whales. 
As a class, mammals are terrestrial; but here we find an 
order which is wholly water-living. They are so far modi- 
fied as to have lost one pair of legs, wholly unfitting them 
for a terrestrial life; and the second pair is modified into 
very efficient paddles. Again, the tail is adapted to swim- 
ming, and the body is covered with a very thick layer of fat 
to protect them from the intense cold met with in their 
habitats. The bowhead whale has no teeth and a very 
small throat, hence cannot live on large animals or on gross 
vegetable bodies. It, however, has an enormously capa- 



MAMMALS 337 

cious mouth with which it takes up great quantities of sea 
water containing countless numbers of small animals. It 
would be unpleasant and not economical to swallow such 
mouthfuls of sea water. Consequently, in place of the teeth, 
there grow these filaments of whalebone from the upper 
jaw that act as a strainer in allowing the water to escape, 
retaining the myriads of small animals for food. 

An elephant's trunk is wonderfully well adapted to the 
needs of that animal. The great tusks prevent the animal 
from reaching the ground with its mouth to pick up food ; 
but the trunk with its innumerable muscles forms a grasp- 
ing organ of wonderful delicacy and flexibility with which 
anything from hay to peanuts or bits of candy may be 
cony eyed to the mouth. 

The members of the cat family catch their prey by 
slipping up and pouncing upon it unawares. For holding 
their prey securely the toes are provided with very sharp, 
hooked claws. However efficient and necessary these claws 
are, they would nevertheless be of very great inconvenience 
were they prominently protruding from the feet. The 
claws would catch in various objects, causing noise, stum- 
bling, and all sorts of annoyances. To avoid this, they can 
be retracted into the folds of the skin and hair, where they 
cannot cause unexpected trouble ; and at the same time this 
retraction makes possible the still, noiseless tread so char- 
acteristic of cats. 

If the whales stand first as showing the most remarkable 
modifications of structure to suit their environments, then 
the bats ought to stand very close to them. It is very 
remarkable that a mammal clothed with hair and without 
feathers should still be capable of very perfect flight. 
Moreover, the bats fly in the night time and do not have 
herrick's zool. — 22 



338 MAMMALS 

highly developed eyes, yet they are so adapted to nocturnal 
flight, because of the great development of the tactual sense 
in the wing membranes, that they easily avoid the objects 
in or near their path. Indeed, it is said, they could do this 
were they totally blind. Again, in most mammals, we find 
the hind pair of legs the stronger ; but in the bats, the front 
pair is the stronger and better developed, which is a direct 
adaptation for flight, since it is these that are mainly con- 
cerned in flight. 

Instances of adaptations among the mammals are almost 
without end, and our space forbids mention of more. 
Much pleasure and profit may be derived from a study of 
the habits of mammals and of the adaptations to meet the 
demands of their environments. 

CLASSIFICATION OF THE EXAMPLES 

Class — Mammalia. 

Subclass I — Prototheria. 

Order — Monotremata. 
Types of Order. 

Ornithorhynchus anatinus — Duckbill. 
Tachyglossus aculeatus or Echidna aculeata 
— Spiny ant-eater. 
Subclass II — Theria. 

Section A — Metatheria or Marsupialia. 
Order — Polyprotodontia. 
Type of Order. 

Didelphys virginiana — Opossum. 
Order — Diprotodontia. 
Type of Order. 

Macropus giganteus — Kangaroo. 
Section B — Eutheria. 
Order — Edentata. 
Types of Order. 






MAMMALS 339 

Cholapus Hoffmani — Two-toed sloth. 

Tolypeutes tricinctus — Three-banded 
armadillo. 
Order — Cetacea. 
Types of Order. 

Physeter ?nacrocephalus — Sperm whale- 

Balcena mysiicetus — Greenland whale. 

Delphinus del phis — Dolphin. 
Order — Sirenia. 
Types of Order. 

Trichechus latirostris — Manatee. 

Halicore australis — Dugong. 
Order — Ungulata. 
Types of Order. 

Rhinoceros unicornis — Rhinoceros. 

Hippopotamus amphibius — Hippopotamu; 

Bos (several species) — Ox. 

Camelus dromedarius — Dromedary. 

Camelus bactrianus — Two-humped camel. 

Lama huanocos glama — Llama. 

Lama huanocos pacos — Alpaca. 

Elephas africanua 



. Elephant. 
Llephas indicus J 

Order — Carnivora. 

Types of Order. 

Procyon lotor — Racoon. 

Ursus americanus — Black bear* 

JJrsus horribilis — Grizzly bear. 

Felis tigris — Tiger. 

Felis leo — Lion. 

Phoca vitulina — Seal. 

Callotaria ursina — Fur seal. 

Odobenus obesus — Walrus. 
Order — Rodentia. 
Types of Order. 

Mus norvegicus — ft at* 

Erethizon dorsatus — Porcupine. 

Cynomys ludovicianus — Prairie dog. 



340 MAMMALS 



Castor canadensis — Beaver. 

Lepus sylvaticus — Rabbit. 
Order — Insectivora. 
Types of Order. 

Sorex personatus — Shrew. 

Scalops aquaticus — Mole. 
Order — Chiroptera. 
Types of Order. 

Lasiurus borealis — Red bat. 

Myotis subulahis — Brown bat. 

Phyllostoma hastatum — Vampire. 

Pteropus edwardsi — Fruit-eating bat. 
Order — Primates. 
Types of Order. 

Lemur macaco — Lemur. 

Cynocephalus anubis — Baboon. 

Simia satyrus — Orang-outang. 

Anthropithecus troglodytes — Chimpanzee. 

Gorilla gorilla — Gorilla. 

Homo sapiens — M^n. 



XXVI. ANIMALS OF THE PAST 

The signs that indicate the existence of prehistoric ani- 
mals. — There are signs, or indications, scattered over the 
earth that denote the past existence of a great host of ani- 
mals different from those now living. This vast assemblage 
of curious and interesting forms was born, lived, and died 
before the present species came to inhabit the land and seas. 
The signs left by these prehistoric creatures consist of bones, 
teeth, footprints, shells, and skeletons that are found in the 
rocky structure of the earth, in quarries, railway cuts, beds 
of streams, and in many other places. We call these signs 
by one comprehensive term, fossils. It is by means of fos- 
sils that we have been able to learn something of this mighty 
and ancient host; and any discussion of the animal king- 
dom would be incomplete without mention of these bygone 
forms. 

Eras of the earth. — Briefly, geologists divide the past 
history of the earth into four great chapters, or, as they are 
called, eras. These are in their order, beginning with the 
oldest, as follows: archean, paleozoic, mesozoic, and ceno- 
zoic. From a zoological standpoint the archean era is 
characterized by a noticeable lack of fossils or any absolute 
indications of animal life. The paleozoic era is prominent 
as an age when invertebrates existed, while the mesozoic is 
characterized by its great number of reptiles. Finally, the 
cenozoic, or last era, is known as the age of mammals. 

341 



342 animals of the past 

Animal Life in the Archean Era 

The word archean means beginning- Therefore, this era 
covers the time of the beginning of the earth's crust and of 
the formation of the oldest rocks. At this time, we hardly 
dare say how long ago, most of the surface of the earth was 
covered with water, and there were no varied and forest- 
covered landscapes to greet the eye. In fact, so far as we 
know, there were no plants large enough to be visible to the 
unaided eye. Indeed, it is not certain that any plants 
existed, The same thing may be said of animals. Almost 
no sure signs or fossils of animal life have been found to 
show that animals existed then. If animals did exist in 
the archean age, they must have been small and probably 
had soft bodies like the amoeba and so were not preserved. 

There are some things, however, that lead geologists to 
think that life did exist in the archean time. For example, 
beds of iron ore and crystalline limestone are found in 
rocks of this era, and these are usually formed through the 
agency of life, but not always. Hence these deposits of 
iron and limestone are not clear proofs. It is also thought 
that some very obscure fossils of a low animal have been 
found; but here again certainty cannot be said to exist. 
The thing that can be stated with surety is, that at the very 
beginning of the next era, the paleozoic, there was an 
abundance of animals of the lower types. Now, since it is 
positively known that animals came into existence through 
a gradual course of development rather than by a sudden, 
simultaneous appearance, we shall have to conclude that 
life did exist in the archean era, since it was so abundant 
at the beginning of the paleozoic. For some reason, all of 
this life and all of its records have been blotted out. 



ANIMALS OF THE PAST 



343 



Animals of the Paleozoic Era 



Now we find ourselves 
on very much surer 
ground. At the usher- 
ing in of this era the 
waters of the earth were 
teeming with myriads of 
animals, all invertebrates. 
Later in the era, for it 
was very long, the first of 
the fishes — an ancient 
type — some amphibians, 
and a few primitive rep- 
tiles came in. So, after 
all, the vertebrate ani- 
mals appeared rather 
early in the geological 
history of the earth. 

Trilobites. — The most 
important animals of the 
early paleozoic were the trilobites 





Fig. 218. — Group of cup corals. 



Fig. 217.— Trilobite. 

members of the branch, 
Arthropoda. The bod- 
ies of these animals were , 
divided into three longi-^ 
tudinal lobes, separated 
by two furrows, some- 
times deep and some- 
times shallow and 
obscure (Fig. 217). The 
trilobites possessed nu- 
merous jointed append- 



344 



ANIMALS OF THE PAST 




ages, and varied from less than an inch to two feet in 
length. They were exceedingly abundant in the first half 

of this era, but later 
slowly declined in num- 
bers and variety until 
they passed out of exist- 
ence by the beginning of 
the mesozoic era, never 
to reappear. 

Lamp shells. — Perhaps 
the next most important 
group of animals was the 

Fig. 219.— Honeycomb coral. lamp shells, Or brachio- 

pocls. They were also very numerous in the seas at this 
time. This group differs from the trilobites in never hav- 
ing entirely passed out of existence, because some species, 
almost unchanged, are living at the present day. 

Corals. — There were corals also in those days. These 
were mainly of three lands : the cup corals, honeycomb corals, 
and the chain corals. 
Their names indicate 
something of their 
shape and appear- 
ance. The cup corals 
were single, solitary 
polyps or groups of 
polyps, each more or 
less cup-shaped (Fig. 
218). The honey- 
comb corals were groups of polpys, each more or less 
polygonal in shape, hence resembling a honeycomb (Fig. 
219). The appearance of the chain corals may be seen 




Fig. 220. — Chain coral. 



ANIMALS OF THE PAST 



345 



from Figure 220. It must be remembered 
that these are all quite different forms from 
the corals living to-clay. 

Crinoids. — Then there were the crinoids, 
or sea lilies (Fig. 221), members of the star- 
fish branch. Here, again, we have an ex- 
ample of a group of prehistoric animals 
some representatives of which are living 
to-day, for a crinoid is sometimes dredged 
from the sea even now. They were much 
more abundant then than at present. 

Mollusks. — Numbers of the mollusks 
existed all through the paleozoic era. They 
were unlike the mollusks of to-day and were 

probably not edible. 




Orthoceras. 



One of them, the 
Orthoceras, possessed 
a straight, tapering Crinoid. 
shell, chambered like the shell of 
the pearly nautilus (Fig. 222). In 
fact, this animal belongs to the 
same class as the nautilus and 
squid. The Orthoceras varied from 
a few inches to ten or twelve feet 
in length. 

Insects. — In the early part of 
the paleozoic era we find signs of 
insect life, if we may call a scor- 
pion an insect. More than this, 
the scorpion is the first air-breath- 
ing animal found in the rocks of 
America (Fig. 223). Later on, in 



346 



ANIMALS OF THE PAST 




Fig. 223. — Fossil scorpion. 



the great coal-forming period 
of this era, we find traces of 
spiders and several kinds 
of insects; namely, locusts, 
cockroaches, and dragon flies. 
Fishes. — Fossils are found 
indicating that fishes came 
into existence early in the 
paleozoic era, although not at 
the beginning. These ancient 
fishes were very different 
from those living to-day. 
Their bodies were, for the 
most part, covered with bony 
plates or smooth, hard, in- 
flexible scales, quite unlike 
the scales on living fishes. 




Fig. 224. — Paleozoic fish. 




Fig. 225. — Paleozoic fish. 



ANIMALS OF THE PAST 



347 



Animals of the Mesozoic Era 

In this era the reptiles increased in size, variety, and 
number. Fishes, insects, and mollusks became abundant 
and various, and more nearly approached the living forms 
of these groups. Sea 
urchins (Fig. 226) 
much like our pres- 
ent ones appeared 
in abundance. The 
lamp shells dimin- 
ished in number of 
species, but the 
squids, cuttlefishes, 
and other mollusks 
appeared and peo- 
pled the seas. Their 
shells are found in 
immense numbers 
and are well preserved. The trilobites having disappeared, 
crabs and lobsters came in their places. 

Reptiles. — It is among these animals that the greatest 
changes are noted. There existed at this time three classes 
of reptiles: land reptiles, sea reptiles, and flying reptiles. 
They were very abundant and of extraordinary size and 
variety. 




Fjg. 226. — Sea urchin of mesozoic limes. 




Fig. 227. — Sea reptile of mesozoic times. 



348 



ANIMALS OF THE PAST 



The remains of about fifty species of sea reptiles have been 
found. Some of them were thirty to forty feet long. 




Fig. 228. — Sea reptile of mesozoic times. 

Figure 227 gives a very good idea of the appearance of one 
species. Another species shown in Figure 228 varied from 
twenty -five to thirty feet in length. 




Fig. 229. — Land reptile of mesozoic times. 



ANIMALS OF THE PAST 349 

It is among the land reptiles that we find the hugest 
animals. Some of them were even larger than the elephant 
and moved sluggishly. Many of them were herbivorous, 
cropping the branches of trees, while others were carnivo- 




Fig. 230. — Land reptile of mesozoic times. 

rous, killing their fellows. Some of them had huge hind 
limbs on which they walked, dragging an immense tail 
behind, and holding the small front legs up like a kangaroo 
(Fig. 229). The one shown in Figure 230 walked on all four 




Fig. 231. — Flying reptile of mesozoic times. 

legs and was sometimes sixty feet long. A species of land 
reptile found in Colorado attained a length of seventy to 
eighty feet. 

More curious still were the flying reptiles. These were a 



350- 



ANIMALS OF THE PAST 



strange combination of bird and reptile. The bones were 
hollow, but there were no feathers on the body. Their 
wings were leathery like those of a bat; and sometimes they 
had a long tail ending in a flap. Figure 231 gives an idea 
of their appearance. 

Figure 232 shows a remarkable reptilelike bird just as its 
outlines were found impressed on the rocks. It had wings, 




Fig. 232. — Reptilelike bird of mesozoic times. 



and the whole body was covered with feathers; but the 
mouth, like that of a reptile, had teeth, and like a reptile 
it had a long, jointed tail with feathers along the sides in 
pairs. This seems to indicate that the reptiles and birds 
have sprung from the same ancestors. 

Birds. — Birds appeared during the mesozoic era. Some 
of them had teeth and some of them had none. They 
varied in size from small birds to those having a height of 



ANIMALS OF THE PAST 351 

six feet. Many of them had no wings but depended on their 
strong legs for locomotion. 

Mammals. — As we have already said, these are the 
highest animals on the earth. They appeared for the first 
time in the early mesozoic. But the first representatives 
were of a low type; and the earliest that have been found 
in this country belong to the marsupials and monotremes, 
the same groups as those to which the kangaroo and duck- 
bill belong, respectively. Toward the end of the mesozoic 
higher types of mammals came into existence. 

Animals of the Cenozoic Era 

We have seen how life began with very low forms in the 
archean, and gradually grew higher and higher by the ex- 




FlG. 266. — Mammoth. Redrawn, by permission, from an illustration 
by Knight in McClure's Magazine, 1900. 

tinction of old and low forms and the formation of new and 
higher forms, until now, in the beginning of the cenozoic 



352 ANIMALS OF THE PAST 

era, we find a great similarity to the life as it now exists. 
The great advance in this era was the remarkable develop- 
ment of mammals. The great reptiles disappeared and 
mammals took their places. In the ocean we find huge 
whalelike creatures seventy feet long. Remains of the 
Zeuglodon have been found in great abundance in Alabama. 
The early ancestors of the cat, panther, wolf, etc., appear in 
this era. The elephant family was represented by the 
huge mammoth (Fig. 233) and mastodon, neither of which, 
however, was much if any larger than some of the largest 
living elephants. Insects and birds were abundant in this 
era. Monkeys, horses, and rhinoceroses appeared in the 
cenozoic. Later came the buffaloes, hyenas, elks, etc. 

The coming of man marked the climax in the progress 
of life upon the globe. Just how, or just when he came, 
we do not know, but we have sure proof that he has 
existed upon the earth many thousands of years. 

Significant features of the history of animal life on the 
earth. — It has been the attempt of the author to show that 
the present animals on the earth are all connected with one 
another, from the lowest to the highest, by intermediate 
forms, and that all life has gradually arisen from a very 
simple, probably one-celled animal. In examining the 
history of the appearance of animals on the earth, we find 
the same thing to be clearly evident. The first form of life 
we found was very simple indeed, and lived wholly in the 
water. This was succeeded in a later age by higher life 
that finally came to live on land. This, in turn, was suc- 
ceeded by higher and higher and more varied forms, until 
it culminated in the appearance of man, the crowning feature 
of life. 



XXVII. THE STRUGGLE FOR EXISTENCE 

The great number of animals born that never reach 
maturity. — Pools of water are often seen that are literally 
black with tadpoles. Is it possible that all of them become 
full grown? If so, the earth would become alive with toads, 
because there are thousands upon thousands of pools con- 
taining polliwogs. Many insects increase in an enormous 
geometrical ratio and if all lived, no other animals could exist 
on the earth. A female codfish deposits from two to six 
millions of eggs in one season. If all these hatched and the 
young cod grew to maturity, the ocean would soon be so 
full that no other fish could find room to live. It is plain 
then that myriads of animals are born that never reach 
maturity. 

The struggle for existence and survival of the fittest. — 
Ever since animals appeared on the earth they have been 
constantly struggling with one another and with their 
surrounding conditions to maintain their existence on the 
earth. Some tadpoles are stronger than others from the 
(start. These stronger ones are able to swim more rapidly, 
hence are able to catch their food before the weaker ones 
can get to it. In this way the strong ones grow stronger, 
and the weak ones weaker, and in the end, only a few of 
the hardier tadpoles are left to reach maturity. It is much 
the same with the insects. Some are better fitted to obtain 
food than others, and some are better protected from their 
enemies and escape being devoured, while others travel far 

353 



354 THE STRUGGLE FOR EXISTENCE 

and meet with less unfavorable surroundings. Thousands of 
the cod's eggs never hatch and thousands of the young cod 
die from disease, while others are killed ; so that but a few 
finally become full grown. The question naturally arises, 
how do any reach maturity and live? 

After long years of patient observation, a law known as 
the " survival of the fittest" has been enunciated and ap- 
parently established. The tadpole and the young codfish 
that could swim the fastest and had the strongest jaws were 
best able to procure food and most likely to survive. All 
animals that are best fitted to meet their surroundings are 
the ones that are most apt to live. In other words, these 
are the fittest animals, and it is these that reach maturity. 

Adaptations to surroundings. — Wherever we may go to 
observe animals, we shall find that the surviving ones are 
those best adapted to their surroundings. For example, a 
tiger with its short hair could not withstand the climate of 
the polar regions so well as the polar bear with its long, 
shaggy coat. The common toad could not exist on .the 
deserts of the great Southwest, but the horned toad and the 
Gila monster prefer these regions because they are adapted 
to them. 

Moreover, animals are being constantly modified and 
molded to suit their changing environments. We do not 
often recognize these changes because they are slight and 
very gradual ; nevertheless, they amount to a great deal in 
a long series of years. For example, many insects have 
been known to change from one kind of food plant to an- 
other after the former had been destroyed. The same 
species of insects and reptiles often differ greatly in color 
when living upon different colored plants or upon earth of 
different shades, probably to gain protection from their 



THE STRUGGLE FOR EXISTENCE 



355 



enemies. In other words, animals are constantly being 
changed, or adapted, to meet their surrounding conditions; 
and those best adapted to their environment are most apt 
to survive. 

Resemblances. — However closely we watch a Caro- 
lina grasshopper flying over a dusty road, we shall have 
great difficulty in finding it after 
it alights, because the color of its 
wings so closely resembles that 
of the dust. Again, we shall have 
difficulty in finding bobwhite in 
the grass or among the weeds, 
no matter how carefully we 
follow his song, because his color 
blends so nicely with the sur- 
roundings. Such resemblances 
enable these animals to escape 
their enemies and are, therefore, 
known as protective resemblances. 
The insects are especially notable 
for their many examples of such 
resemblances. 

An excellent instance of such 
a resemblance is found in the 
case of the katydid. In this 
insect the wings resemble leaves 
so closely in color and appearance as to deceive the 
most observant. In fact, all katydids have wings that re- 
semble leaves more or less in appearance. Those insects 
familiarly known as walking sticks are very easily mistaken 
for the branches of the trees on which they live. Some 
have irregular outgrowths on the body and limbs which 




Fig. 234.— Walking stick in- 
sect with projections on its 
body and legs like those on a 
rough branch. 



356 



THE STRUGGLE FOR EXISTENCE 



cause them to resemble twigs still more closely. See Figure 
234. 

The caterpillars of certain moths known as the looping 
caterpillars, or measuring worms (Fig. 235) , show a re- 
markable resemblance to 
the branches on which they 
live. They are colored like 
the bark and have the re- 
markable habit of holding 
fast by their false hind legs, 
while the long slender body 
projects outward like a 
twig. 

Perhaps one of the most 
remarkable resemblances is 
the Kallima, or leaf butter- 
fly, of India. Figure 236 
shows the remarkable simi- 
larity of this insect to a 
leaf. When it alights on a 
branch, its wings are held 
vertically with the upper 
sides folded together so 
that only the under sides 
show. Note the dark line 
running through the middle 
of the wings like the midrib 
of a leaf. Note also the 
small projection on the end 
of the wing that resembles the petiole of a leaf. The legs 
are usually more or less hidden, and, more than that, are 
so colored that they are inconspicuous. The upper sides 




Fig. 235. 



Looping caterpillar on a 
branch. 



THE STRUGGLE FOR EXISTENCE 



357 



of the wings are dark, with purple and orange markings, 
so that when flying, the butterfly is quite conspicuous. 

Then, again, there are the small green snakes that live 
in the grass; the earth-colored snakes that live along the 
bare roadsides or in 
bare fields; the tree 
frogs that have grown 
to imitate the bark 
of the trees on which 
they live or, if they 
live among the leaves, 
then have grown to 
resemble the leaves 
in color. 

A very interesting 
and remarkable case 
of protective resem- 
blance is seen among 
those animals in which 
there is an actual 
change of color of their fur coats to correspond to the 
season. The American hare (called the white rabbit) in 
summer is of a cinnamon brown; but, as winter comes 
on, its coat turns to a white color. 

Again, certain spiders that live in flowers are colored like 
the flowers, so that they remain hidden and lie in wait to 
catch their prey of unsuspecting insects that visit such 
flowers for nectar. Such resemblances are known as ag- 
gressive resemblances. 

Mimicry. — In the struggle for existence, the weaker or 
more vulnerable animal often happens to vary in such a 
manner that it resembles a stronger or more aggressive 




Fig. 236. — Kallima. 



358 



THE STRUGGLE FOR EXISTENCE 



animal. This resemblance is a protection, because the 
weaker animal is taken by its enemies for the animal which 
it resembles, and consequently goes unharmed by them. 
The succeeding generations of the weaker animal come 
more and more to imitate the stronger, until, finally, we 
ourselves have difficulty in distinguishing one from the 

other. A butterfly, 
known as the vice- 
roy, imitates another 
and larger butterfly, 
known as the mon- 
arch. The monarch 
has reddish brown 
wings, two inches 
long, with black 
veins. It also has a 
peculiar odor which 
is very much disliked 
by birds, hence it is 
let alone by them. 
Now, if another but- 
terfly should grow to 
look like the mon- 
arch, even though it 
had no peculiar odor, it would be less liable to be eaten by 
birds, because the birds, having grown to know the monarch, 
would think that this other butterfly was also a monarch 
and would let it alone. Exactly this thing has happened. 
The viceroy has grown to resemble the monarch so closely 
that only a very observant person can tell them apart, 
and probably birds do not know one from the other, hence 
touch neither. See Figure 237. 




Fig. 237. — 'Monarch butterfly above and vice- 
roy below. Note the resemblance. 



THE STRUGGLE FOR EXISTENCE 359 

Certain flies, known as syrphus flies, imitate bees in color, 
size, and general appearance so closely as to deceive ex- 
perienced people^ 

Many examples might be given of the manner in which 
animals are protected from other and stronger ones. In the 
same way, animals are provided with means of protection 
against climate, scarcity of food, etc. Those animals living 
in cold climates are provided with thick coats of fur, 
feathers, or hair. Those that hibernate throughout the 
winter lay up during the summer a large amount of fat, 
to act as food when none is obtainable. 



XXVIII. LIFE PROCESSES OF ANIMALS 

In our study of the animal kingdom we have seen that 
certain processes, necessary to the life of the individual and 
to the perpetuation of the species, go on in the body of 
every animal. Since the life of the animal and the future 
existence of its kind depend upon these processes, they have 
been termed the life processes. Among the more important 
are ingestion, digestion, secretion, excretion, respiration, 
circulation, and reproduction. 

Ingestion. — The combined activities of procuring, mas- 
ticating, and swallowing food may be termed ingestion. 
Without food, the animal would soon die. Therefore, 
every animal is provided with some means of obtaining it 
and passing it to the organs of digestion. When the amoeba 
touches a bit of food, the protoplasm of the body simply 
incloses the particle, for this animal has no mouth or special 
organs for ingesting food. The cilia of the Paramecium 
and vorticella create currents of water that bring food into 
the mouth. Food is brought to the sponges by the currents 
of water flowing through the body. The hydra, sea anemone, 
and coral polyps gather food and pass it into the mouth 
with the tentacles. The tapeworm absorbs its food through 
the skin, but the earthworm swallows quantities of soil 
from which the food particles are extracted. Insects have 
biting and sucking mouth parts for obtaining their food. 
Fish have jaws armed with teeth, while toads collect their 
food with the tongue and swallow it whole. The snakes 

360 



LIFE PROCESSES OF ANIMALS 361 

hold their prey with their teeth, which point backward and 
swallow their food whole, but the birds have bills with which 
they pick up their food. The mammals, as a rule, possess 
teeth fitted either for tearing or grinding and therefore the 
food is usually masticated. 

Digestion. — Among the most important organs in the 
body are those that carry on the processes of digestion. The 
number, size, structure, and appearance of the organs of 
digestion vary greatly in the different groups of animals. 
For example, none of the one-celled animals possess dis- 
tinct organs of digestion. The food of these animals is 
digested anywhere in the protoplasm. In the sponges 
there are no distinct digestive organs, but individual cells 
gather and assimilate their own food. The hydra has no 
alimentary canal, but some of the cells of the endoderm 
secrete, within the body cavity, a digestive fluid that acts 
upon the food. The echinoderms and worms offer the first 
examples of animals with a fully developed digestive tract, 
or tube. The earthworm has a well-defined alimentary 
canal surrounded by the perivisceral space, or ccelome. 
It consists of several distinct parts and is quite similar to 
that of the locust. The digestive organs of the different 
members of the Mollusca vary in number and development, 
but in the clam there is a mouth, an esophagus, a stomach, 
and an intestine. The alimentary canal is most highly 
developed in the vertebrates. In the rabbit, for example, 
it consists of three main divisions : esophagus, stomach, and 
intestine. Moreover, a liver and a pancreas are present as 
appendages of the canal, but these are organs of secretion. 

Secretion. — There are certain organs in the bodies of 
the higher animals known as glands, that take special food 
materials from the blood and elaborate them into products 



362 LIFE PROCESSES OF ANIMALS 

which are useful in carrying on the work of the body. 
These glands are the organs of secretion and the chief ones 
are connected with the digestive tract and perform very 
important functions in the process of digestion. For ex- 
ample, the salivary glands opening into the mouth, where 
the saliva dissolves and moistens the food and, in some 
animals, acts upon the starch, changing it into sugar. In 
the walls of the stomachs of the higher mollusks and the 
invertebrates there are glands called gastric follicles that 
secrete the gastric juice. In the Protozoa there are no 
special glands for secreting digestive fluids and the whole 
work of digestion is accomplished by the protoplasm. The 
same may be said of the sponges and hydra? except that 
in the latter certain cells of the endoderm secrete a diges- 
tive fluid. The liver and pancreas are two very important 
organs of secretion connected with the alimentary canal 
of many animals. The liver of vertebrates is the largest 
gland in the body. It secretes bile, the work of which is 
imperfectly understood, but it certainly performs an im- 
portant function in digestion. 

Excretion. — There are two antagonistic processes going 
on in the bodies of all animals during life; namely, a build- 
ing-up process and a tearing-down process. In the tearing- 
down process, waste materials are given off into the fluids of 
the body — blood in those animals that have blood. These 
waste materials, which consist mainly of carbonic acid, 
water, and urea, must be thrown off from the body, or 
excreted. In the vertebrates, they are thrown off by 
the lungs, skin, and kidneys. In the lower animals, we do 
not find all of these special organs of excretion. For 
example, the amoeba excretes carbonic acid through the 
surface of the body and the pulsating vacuole aids in excret- 



LIFE PROCESSES OF ANIMALS 363 

ing other substances. In the sponges the cells lining the 
canals give up their products of excretion to the water and 
are thereby carried out of the body. Excretion is carried 
on through the surface of the body wall in the hydra. In 
the starfish there is a system of tubes containing a fluid 
(mostly water) that probably acts as an excretory apparatus. 
Moreover, the respiratory caeca act as organs of excretion. 
In the earthworm the nephridia and skin get rid of the 
waste materials, while the tracheae and malpighian vessels 
are the excretory organs in insects. The nephridia of 
worms and the malpighian vessels of insects are comparable, 
in their work, to the kidneys of vertebrates. Respiration 
is a method of excretion and an exceedingly important life 
process. If it is completely arrested, death ensues. It is 
carried on very differently by different animals, as has been 
shown. Respiration is most highly developed and effec- 
tually carried on in those animals that breathe by lungs, 
especially the birds and the mammals. 

Circulation. — The food that an animal eats and digests 
must be distributed throughout the body in order that the 
different organs may obtain nutriment for building up worn- 
out tissues and for the development of energy to accom- 
plish work. Moreover, the waste material produced in all 
parts of the body must be brought to the lungs, skin, kid- 
neys, and other excretory organs to be thrown off. In the 
higher animals the. food is distributed and the waste matter 
brought to the excretory organs by a fluid (blood) circulat- 
ing through a system of tubes. The whole process is known 
as circulation. There is no definite system of blood vessels 
among the lower animals until the echinoderms are reached. 
In the Protozoa, the food circulates through the endosarc. 
The currents of water distribute the food to the different 



364 LIFE PROCESSES OF ANIMALS 

parts of the sponge's body, while in the bodies of the hydrse, 
sea anemones, and polyps the food circulates in the fluid 
of the body cavity. But in the jelly fishes there is a system 
of tubes (not blood vessels) branching off from the stomach, 
as we have seen, through which the food is carried directly 
to the various parts of the body. The first approach to a 
true circulatory system is made by the starfish and sea 
urchins. The earthworm possesses a better defined cir- 
culatory system but has no true heart. Many members 
of the Arthropoda and Mollusca present a well-defined cir- 
culation, but it is among the vertebrates, especially birds 
and mammals, that we find the highest types of circulation. 

Reproduction. — To insure its existence and to prevent 
its extinction every species of animal is endowed with the 
power to reproduce itself. There are two methods of re- 
production among animals; namely, asexual and sexual. 
Only the lower animals reproduce asexually. The great 
majority of animals, if not all, reproduce sexually. There 
are also two methods of asexual reproduction; namely, 
fission and budding. In asexual reproduction by fission 
the animal simply divides in two parts. Fission takes place 
in the Protozoa, in some ccelenterates, and in some worms. 
In asexual reproduction by budding, a budlike protuberance 
forms on the side of the body of the parent animal. The 
bud grows and gradually develops into a mature form which 
may or may not remain attached to the parent animal. 
Reproduction by budding takes place among the sponges, 
Ccelenterata, some worms, and ascidians. 

The most universal and important method of reproduc- 
tion among animals is the sexual method, which consists 
in the union of two cells, the sperm (male) cell and the egg 
(female) cell. Among the vertebrates, in most arthropods 



LIFE PROCESSES OF ANIMALS 365 

and echinoderms, and in some mollusks and worms these 
cells emanate from two different individuals, male and 
female. Both kinds of cells may be produced by the same 
individual. For example, each earthworm produces both 
the sperm cell and egg cell. Hydrse, sea anemones, jelly- 
fish, and many worms are bisexual; that is, produce both the 
sperm cell and egg cell. After the sperm cell unites with, 
or fertilizes the egg cell, development of the embryo begins. 
The process of growth has been described in Chapter III. 



XXIX. THE GEOGRAPHICAL DISTRIBUTION 
OF ANIMALS 

Geographical distribution. — We visit menageries with 
the keenest interest to see strange animals from strange 
countries. It is evident from a moment's thought that 
different countries are the homes of very different animals. 
For example, the lion is found in Africa, the kangaroo in 
Australia, the boa constrictor in South America, and so on 
through a long list of examples that might be cited. In 
North America we find the coyote, the black bear, and the 
rattlesnake; but we do not find them in Europe. In the 
United States, we find the grizzly bear in the Rocky Moun- 
tains, but not in New England, or the southern states. 
Again, the alligator is found in the swamps of the Gulf 
states and nowhere else in the United States. Thus we 
see that some animals, at least, live in certain well-defined 
areas of the earth's surface, and it is easy to make a map, 
showing the areas of the country in which many animals 
are found. 

When the extent and location of the areas, or regions, 
occupied by an animal have been ascertained, the geograph- 
ical distribution of that animal may be said to have been 
determined. 

Questions arising from the distribution of animals. — 
Animals vary greatly in their ability to go from one place 
to another. For example, a wild goose can go from Canada 
to Florida much easier than a pond snail. There are also 

366 



THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 367 

barriers that prevent animals from going from one region to 
another. Finally, after an animal has reached a region far 
from its original home, it is liable to become profoundly 
changed in habits, character, and, possibly, in structure. 

Why is it that certain animals occupy certain areas? 
How do they pass from one region to another? What 
retains animals within the boundaries of certain areas? 
How are animals modified when they migrate to new areas ? 
These are some of the questions that arise from the study 
of the distribution of animals. 

Means of dispersal. — One of the most universal means 
by which animals are distributed from one region to an- 
other is through the agency of man. For example, the eel 
has been put into many ponds and streams of the United 
States that it could not have reached except by the aid of 
man. The horn fly, a serious pest to cattle, was brought 
over from Europe, probably in ships with live stock. By 
the same agency, the English sparrow and even the horse 
have been brought to America. 

Birds can fly from one region to another, across wide 
expanses of water or over high mountain ranges. Fish can 
swim to widely remote parts of the sea. Many mammals 
can swim across narrow seas, rivers, etc. Some mammals, 
notably the whales and the seals, can swim for leagues at 
sea. Mammals are sometimes carried on floating masses 
of vegetation to islands in the sea. Birds are blown across 
seas by high winds. The bodies of some animals, as roti- 
fers and infusorians, may become so dry and light that they 
are carried by winds. Insects are often carried on birds' 
feet, blown by the wind, or floated on the water in logs of 
wood, etc. Worms crawl, frogs and toads leap, snakes 
swim and crawl. 



368 THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 

Barriers to dispersal. — The barriers that prevent or 
retard the migration of animals from one region to another 
may be roughly classed as land, water, and climatic barriers. 
Of course, land is a barrier in the strictest sense only to 
those animals that live in the water. For example, it is 
easy to see that a fish on the coast of California would be 
forever debarred from entering the Gulf of Mexico by the 
Isthmus of Panama, narrow though it be. Likewise, fish 
living in inland seas without outlets are forever debarred 
from leaving them of their own free will. In two rivers 
running side by side, and emptying into the ocean, there 
may be fish that will never get from one to the other, owing 
to the narrow strip of land between. 

Deserts are barriers to the dispersal of many animals. It 
is true that this is due to the absence of water more than to 
any other cause, yet they are land barriers. 

Falls in streams are barriers to the distribution of fish. 
For example, eels could never have reached the Great 
Lakes over Niagara Falls, unless they had been aided by 
man. Mountains present strong hindrances to the migra- 
tion of animals. Especially is this true of ranges that are 
capped with snow. The mammals of California differ in 
some species from those on the eastern side of the Rockies. 

Perhaps, on the whole, water is a more serious barrier 
to a greater number of animals than any other barrier noted. 
The ocean is a barrier to many birds; and birds are probably 
best fitted for migration of any animals in existence. A 
small river will hold a race of monkeys in confinement in a 
given area. Many animals, however, can swim across wide 
streams. The effect of water as a barrier is well shown by 
a study of the animals on an island separated from the 
mainland by a deep channel. The island of Madagascar is 



THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 369 

a noted case. This island is separated from the mainland by 
a channel of water about two hundred and thirty miles in 
width. On this island nearly all of the species of animals 
are different from those in Africa. Moreover, the species 
of birds differ from those only two hundred and thirty miles 
away. 

Salt water is a firm barrier to fresh- water animals. Thus 
the fresh-water animals living on an island not two hundred 
yards from the continent would be effectually debarred 
from swimming to that continent. On the other hand, 
there are many fish living in salt water that are debarred 
from entering fresh-water lakes. 

The third great class of barriers may be called climatic , 
which will include the effects of temperature, moisture, and 
dryness. 

There is a great difference between the animals of the 
tropics and those of the arctic regions. A leopard with its 
short hair would never venture into the arctic region. On 
the other hand, a polar bear would be exceedingly uncom- 
fortable in India. The parrots of Brazil would die in Canada. 
The sloths, ant-eaters, and monkeys of the tropics would not 
survive in the north. Neither would the foxes, sables, and 
minks of Canada be able to live long in Central America. 

As to the effects of moisture and dryness recall the toad. 
On account of excessive evaporation from its skin it demands 
a moist atmosphere and could not survive on the deserts 
of the Southwest. On the other hand, the Gila monster 
would find it extremely distasteful to five in the valley of the 
Mississippi. 

Notwithstanding all these barriers to the distribution of 
animals, every species is unconsciously forced to spread over 
larger areas or pass out of existence. For, in time, a species 



370 THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 

becomes too abundant in a certain area and those on the 
outskirts venture farther and farther in search of food. 
Often a species is driven out by enemies, change of climate, 
etc. In such cases, it may pass over barriers that hereto- 
fore seemed impassable. 

Fauna. — Briefly speaking, the fauna of a.region consists 
of all the animals naturally found in that region. For 
example, the fauna of New York or Mississippi would be all 
the animals found in each respective state. The faunae of 
two adjoining states are usually very much alike, because 
the conditions are about the same, and, usually, there are 
no great barriers between. On the other hand, the faunse 
of two widely separated states like New York and Missis- 
sippi are considerably unlike. This is due largely to the 
difference in climate. 

Faunal areas. — A faunal area is, of course, the area or 
region occupied by a certain fauna. For example, we may 
consider the state of Colorado with its fauna as a faunal 
area. It has been shown above that the relation of faunal 
areas to each other depends first upon their proximity. 
Secondly, it will depend upon the barriers between these 
faunal areas. For example, the fauna of the Island of Mada- 
gascar differs greatly from that of Africa, because of the 
water barrier between. The fauna of California differs 
much from that of the states separated from it by the 
mountains. 

In traveling from the Atlantic to the Pacific, across the 
United States, three fairly distinct regions as regards the 
fauna will be noticed. The moist, temperate region along 
the Atlantic and in the Mississippi Valley, with its charac- 
teristic animals, constitutes the first region. Then, as we 
reach the high plateaus of the Rockies, dry and treeless, 



THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 371 

we shall find that the animals of the Atlantic region have 
been replaced by forms quite different. Finally, after 
climbing the Sierra Nevada, and descending into the Pacific 
region, another assemblage of animals differing from either 
of the above — but not so markedly from the second — 
will be found. It must be borne in mind, however, that 
there is no distinct dividing line between these faunal areas. 
The first overlaps the second, the second the third, and vice 
versa. 

The North American continent as a whole, exclusive of 
the circumpolar region which is common to Asia and 
Europe, may be divided into three primary faunal areas. 
Beginning at the North Polar sea these are as follows: 
the Boreal Region, the Austral Region, and the Tropical 
Region. Here again the areas are not sharply defined, for 
the adjacent ones overlap each other and animals common 
to one are found in the other. 

Faunal areas of the earth. — The earth, as a whole, has 
been divided into seven — some authorities make eight — 
great areas. These are the Arctic, the North Temperate, 
the South American, the Indo-African, the Madagascar, the 
Patagonian, and the Australian. The differences between 
the faunae of these various areas are due to the climate and 
the barriers between them. 

The manner in which the distribution of animals has 
affected species. — It has already been shown that there 
is a tremendous struggle going on between animals all the 
time. By this struggle, many are killed, and many* are 
driven out of certain regions to seek other regions where 
competition is not so great. Thus there is a constant tend- 
ency among animals to distribute themselves over the earth 
in search of conditions more favorable to their existence. 



372 THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 

As a result of this intense struggle, an animal may be 
crowded across a barrier into a region entirely new to it, 
where the conditions are so extremely favorable for its 
growth and increase that it may become strong enough .and 
numerous enough to actually drive out or kill another 
closely allied species existing in that region. For example, 
the black rat was introduced into America from Europe 
about 1544. The conditions here were so favorable that 
it increased in such numbers as to aid very materially in 
crowding out and annihilating our species of native rats. 
Later, in 1775, the brown rat was brought over to America. 
It, in turn, throve prodigiously, and practically exterminated 
the black rat, but remains as our common pest of barns and 
outbuildings. Hence one result of the distribution of ani- 
mals is the extermination of species. 

Another result of the distribution of animals may take 
place that will be exactly the opposite of the one just de- 
scribed. Suppose a short-haired, semi-tropical animal 
living in Mexico should be forced by degrees northward into 
Canada. One must bear in mind that this forced migration 
must be very slow and must extend over a long period of 
time. It is conceivable that, as this species went north- 
ward, the hair of the individuals of successive generations 
would gradually grow longer and longer to adapt them to the 
changed conditions of the climate. By the time the animal 
reached Canada it might be so changed in regard to its 
hair and organs of the body as to have become a distinct 
species. In other words, when an animal is forced across 
a barrier into a new region, the process of adaptation to sur- 
roundings and of natural selection may produce an en- 
tirely new species. Hence a second result of the distribu- 
tion of animals is the formation of new species. 



THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 373 

Other significant features of the distribution of animals. — 

A knowledge of the distribution of animals aids us very 
much in determining the history of the earth. For example, 
if we find a species of animal " having few or no facilities 
for dispersal," on both sides of a very important barrier, 
we feel pretty sure that there was a time in the history of 
the earth when that particular barrier did not exist. Be- 
cause, if it had always been in existence, the species of ani- 
mal mentioned would not be found on both sides, since 
the animal could not pass over the barrier. Hence a 
knowledge of the distribution of animals often leads to the 
disclosure of very profound changes in the topography of 
the earth's surface. To illustrate, take one of the fresh- 
water crayfishes of Great Britain. The same species is 
found on the continent of Europe. Now, since this cray- 
fish cannot pass across the salt water barrier of the English 
channel, it would seem to indicate that this barrier did not 
exist at some former time. In such a case, Great Britain 
would have been simply a part of Europe. As a matter of 
fact, such is the case, as has been proved by other and con- 
clusive evidence. 



XXX. THE HISTORY OF THE SCIENCE OF 
ZOOLOGY 

The study of animal life began long before the Christian 
Era. The Greeks, especially Aristotle, acquired a wide 
range of knowledge concerning a great variety of animals; 
but this knowledge consisted of a mass of isolated and un- 
connected facts that led to no systematic outline of the 
animal kingdom. As a well-grounded science, zoology has 
not existed much over two hundred years, although the in- 
formation concerning animals and animal life gained prior 
to that time included valuable and reliable facts concerning 
a wide range of forms. 

Aristotle. — Aristotle (384-322 B.C.), the eminent Greek 
philosopher, by his own researches and observations, 
gathered together an immense array of facts regarding 
animals, some of which were remarkably accurate and some 
of which were curiously incorrect. He wrote several 
treatises on zoological subjects among which are The His- 
tory of Animals, The Generation of Animals, and The 
Parts of Animals. He divided the animal kingdom into 
two great groups; namely, one containing those forms that 
possessed blood and another including the forms without 
blood. 

Pliny. — After Aristotle came Pliny, the elder, who lived 
in the first century and wrote a natural history which dealt 
with the whole realm of nature — plants, animals, minerals, 
stars, etc. He cannot be regarded as an original worker 

374 



THE HISTORY OF THE SCIENCE OF ZOOLOGY 375 

but rather as a compiler of facts, amid some fables, the 
former borrowed largely from Aristotle. After Pliny's 
time the sciences declined and up to the sixteenth century, 
with few exceptions, no contributions of note were made 
to the science of zoology. 

Sixteenth century. — During the sixteenth century there 
came a revival of the study of animals instituted chiefly 
by the interest in the anatomy of the human body. During 
this period, Conrad Gesner published (1551-1558) his 
Historia Animalium, a work of forty-five hundred folio 
pages, in which he recognized four groups of animals : 
viviparous quadrupeds, oviparous quadrupeds, birds, aquatic 
animals and serpents. Fabulous monsters were yet be- 
lieved in, for he illustrated winged dragons, many-headed 
hydrae, and crowned basilisks. 

Seventeenth century. — In this century came a man whose 
name will be inseparably linked with zoology for all time. 
This was William Harvey who, in 1616, discovered and 
demonstrated the circulation of blood. The discovery of 
this truth must be accorded one of the greatest scientific 
events of all time. Moreover, Harvey studied the embryol- 
ogy and development of the chick and his contributions to 
this phase of zoology are exceedingly important. Again, 
in his famous phrase "omne vivum ex ovo," he enunciated 
the principle that all living things arise from an ovum. 

During the period from 1590-1600 Hans and Zacharias 
Janssen invented the compound microscope and, later, in 
the seventeenth century, it was perfected so as to aid very 
greatly in the study of animal structure and embryology. 
Malpighi first studied the development of the chick with the 
microscope, discovered and described certain organs of in- 
sects — malpighian vessels — with which his name is still 



376 THE HISTORY OF THE SCIENCE OF ZOOLOGY 

connected, and made other histological contributions to 
zoology. Leeuwenhoek, a Dutch investigator, discovered 
blood corpuscles and striated muscle fibers, watched the 
circulation of blood in the tail of a tadpole, thus confirm- 
ing Harvey's discovery, and described many forms of 
Protozoa, rotifers, and hydrse hitherto unknown. Swam- 
merdam, another Dutchman, is known to all entomologists, 
for he studied and described the habits, metamorphoses, 
and anatomy of many different insects, accompanying his 
descriptions with illustrations. Just here must be men- 
tioned the two Englishmen, Hood and Grew, who dis- 
covered, in the tissues of plants, minute cavities filled with 
fluid and surrounded by walls which they termed cells. 

Passing over other and lesser investigators we come to the 
English clergyman, John Ray, who first systematized the 
zoological knowledge already gained and put the science 
of zoology on an organized basis. He grasped the idea of 
species and saw the real value of a comparison of anatomical 
characters of animals to show their true relationships, which 
enabled him to classify animals much better than they had 
been heretofore. 

Eighteenth century. — The year 1707 saw ushered into 
the world the Swedish founder of modern systematic zool- 
ogy, Carl Linne, or Linnaeus. He first established the value 
of groups higher than species — genera, orders, and classes 
— and used them in their proper relation to each other. 
He also instituted the system of naming animals according 
to the principles of the binomial nomenclature. That is, 
each animal was given two names taken from the Latin 
language, the first name indicating the genus and the second 
name the species to which the animal belonged. Linnaeus 
also named and described each species of animal and 



THE HISTORY OF THE SCIENCE OF ZOOLOGY 377 

plant with which he came in contact and published all of 
his observations and principles in a work entitled Systema 
Naturce, of which thirteen editions have been published. 
"By universal consent the Systema Naturae is taken as a 
starting point by sy sterna tists." The names of Bonnet, 
Heller, and Hunter were prominent in zoology in the 
eighteenth century. As a naturalist, the name of Gilbert 
White stands preeminent, and his book, Natural History 
and Antiquities of Selborne, is a classic both in science and 
letters. However, the remaining name to which we must 
give more than passing notice is that of Buffon. Buffon 
was essentially a philosophical zoologist and was the first 
of the great evolutionists. At this time it was held and, in 
fact, could not with personal safety be disputed, that all 
the different species of animals were immutable, or un- 
changeable, and that each was created just as it then ap- 
peared. On the other hand, Buffon promulgated the idea 
of the mutability of species. He held that species of ani- 
mals did not forever remain stable and fixed, but that they 
gradually changed from one form to another so that new 
species were continually being developed from existing ones. 
In other w T orcls, he believed in the principle of evolution, 
although he was not the first to announce such a doctrine. 
Transition from the eighteenth to the nineteenth cen- 
tury. — Buffon was followed (1774-1829) by Lamarck, a 
Frenchman, who held the same views in regard to the 
mutability of species although he ascribed different causes 
for the changes that produced new forms. Lamarck held 
that there was a unity * in the animal kingdom and that all 

1 According to the prevailing conception of his time, Lamarck held 
the view that the animal kingdom presented a serial arrangement, 
which differs markedly from the modern view. 



378 THE HISTORY OF THE SCIENCE OF ZOOLOGY 

the different forms had developed by slow but gradual 
changes from the lowest, or primitive form. In .their 
general views, Buffon and Lamarck were supported by 
another eminent French zoologist, Geoffrey St. Hilaire. 
But the views of these three men exerted little influence 
during their time, owing to the work and writings of Georges 
Cuvier. Cuvier (1769-1832) was a great zoologist and com- 
pletely dominated the science of zoology for half a century, 
especially in France, where he lived and taught. He was a 
profound student of the anatomy of animals and formed a 
classification of animals founded upon their comparative 
structures. He rejected the idea of the unity s; of the animal 
kingdom and held that there were four distinct and inde- 
pendent types of animals, not connected with each other 
by intermediate forms, living or fossil. 

Nineteenth century. — In 1838 Schleiclen enunciated the 
cell theory for plants according to which all parts of the 
body are built up either of cells or of tissues derived from 
cells. Closely following him, Schwann propounded the same 
theory for the animal body. In 1827 Von Baer discovered 
the ovum of mammals, and later, from 1843 to 1846, 
Barry established the relation of the male reproductive 
cell (sperm) to that of the female reproductive cell (ovum) 
by actually observing the union of the two, thereby deter- 
mining the meaning of fertilization. 

In the early part of the last half of the century — 1859 — 
occurred what may fairly be called the most important event 
in the history of biological science, the publication of Charles 
Darwin's Origin of Species. Up to this time the ideas of 
evolution advanced by Buffon, Lamarck, St. Hilaire, and 
Erasmus Darwin had not received general recognition among 
zoologists, to say nothing of the great mass of teachers. 



THE HISTORY OF THE SCIENCE OF ZOOLOGY 379 

writers, and scholars. But with the Origin of Species began 
a storm of discussion and debate out of which there has 
arisen a calm and sane acceptance of the gradual develop- 
ment of the various forms of plant and animal life by a pro- 
cess of evolution. Darwin gathered such a mass of facts 
and marshaled his proofs in such a clear, logical manner 
that the world could not deny the force of his arguments or 
escape the convincing power of his conclusions. 

From 1850 to the present time, the contributions to the 
science of zoology have been steadily increasing in number 
and value and very great additions have been made to our 
knowledge of the subject. The perfecting of the com- 
pound microscope, together with the modern methods of 
research, has given a profound insight into the structure 
of the animal body, disclosed much concerning the func- 
tions of .the various organs, revealed the process and some- 
thing of the significance of reproduction, and added vastly 
to our knowledge of animal life. 

For a fuller knowledge of the history of zoology, one should be- 
come acquainted with the life work of Wotton, of Vesal, Trevira- 
nus, Goethe, Wolff, Von Baer, Siebold, Erasmus Darwin, A. R. 
Wallace, Agassiz, Owen, Haeckel, Huxley, Weismann, and others. 



INDEX 



Abdomen of spider, 147. 

Abomasum, 321. 

Aboral surface, 90. 

Adaptations to surroundings, 354. 

Agassiz, Louis, 379. 

Aggressive resemblances, 357. 

Alligators, 263, 264 ; characteristics 
of, 265. 

Alpacas, 322. 

Alternation of generations in Aurelia 
and campanularian hydroid, 60. 

Amblystoma, 239. 

Ambulacral grooves, 90. 

Ambulacral spines, 90. 

Amceba, 10, 13, 360 ; structure of, 14 ; 
locomotion of, 14 ; manner of eat- 
ing, 15 ; elimination of waste mat- 
ter, 15 ; breathing of, 16 ; sensation, 
16. 

Amphibia, 229 ; characteristics of, 
241 ; adaptations of, 242 ; relation- 
ships of, 243 ; economic importance 
of, 244 ; classification of, 245. 

Anaconda, 251. 

Animals, similarity of, to plants, 8, 9 ; 
beginning of, 19 ; growth of, 21 ; as 
machines, 23 ; classification of, 24, 
28; distribution of, 371. 

Annulata, 75 ; classification of, 88. 

Anopheles, 184. 

Ant-eater, spiny, 312. 

Antenna, 157. 

Ants, 188, 189. 

Aortic arches of earthworm, 81. 

Apteryx, 292. 

Arachnida, 144 ; economic impor- 
tance of, 152 ; characteristics of, 152. 

Archean, 342. 

Aristotle, 374. 

Armadillos, 315. 

Arthropoda, 124. 

Asexual reproduction, 362. 

Atoll, 58. 



Auks, 280 ; great, 280 ; nesting hab- 
its of, 293. 
Aurelia, 52 ; life history of, 53. 
Axolotl, 244. 

Baboon, 333. 

Baer, Karl Ernst von, 378. 

Baleen, 317. 

Barbs, 271. 

Barbules, 271. 

Barnacles, 135. 

Basilisks, 375. 

Bats, 331; fruit-eating, 332; vam- 
pire, 332. 

Bears, black, 324 ; grizzly, 325. 

Beavers, 328. 

Bees, 188 ; small carpenter, 193 ; 
large carpenter, 193 ; leaf-cutter, 
193 ; bumblebee, 193. 

Beetles, 186 ; Colorado potato, 187 ; 
May, 187. 

Bilateral symmetry, 76. 

Bipinnaria, 100. 

Birds, 268; characteristics of, 292; 
molting of, 292 ; incubation of, 292; 
nesting habits of, 293 ; migration 
of, 295 ; adaptations to environ- 
ments, 296 ; economic importance 
of, 297; classification of, 299; 
fossil, 350. 

Bisexual reproduction, 363. 

Blastophaga, 196. 

Blister beetles, 188. 

Blowfly, 186. 

Blow hole, 318. 

Blubber, 318. 

Bluejay, 291. 

Boa constrictor, 251. 

Bobwhite, 286. 

Bonnet, 377. 

Bowfin, 217. 

Brachiolaria, 100. 

Brachiopods, 344. 



381 



382 



INDEX 



Brain of crayfish, 130 ; of perch, 213. 

Branch defined, 27. 

Branchiae, 91. 

Brittle stars, 95. 

Budding, reproduction by, 362. 

Buff on, 377. 

Bugs, 175; squash, 175, 176. 

Bullbat, 289. 

Bullfrog, 240, 244. 

Bumblebees, 193. 

Bureau of Fisheries, 226 ; of Ento- 
mology, 196. 

Butterflies, 178, 179, 180; swallow- 
tail, 180 ; monarch, 180, 356 ; vice- 
roy, 358. 

Buzzard turkey, 286. 

Caeca, pyloric, 91. 

Caecilians, 237. 

Caecum, 306. 

Camel, 322. 

Campanularian hydroids, 50. 

Canals, radial, 38, 92 ; ring, 92 ; stone, 

92 ; inhalent, 38. 
Capillaries, 129. 
Carapace, 124, 262. 
Carbon, 7, 8. 
Carmine, 196. 
Carnivora, 323. 
Carpet beetles, 188. 
Carrion crow, 286. 
Cassowary, 280. 
Cat, classification of, 28. 
Catfish, 217. 
Caviar, 218. 
Cells, number of, 10; nature of, 11 ; 

defined, 17 ; plant, 12 ; animal, 13. 
Cellulose, 7. 

Cenozoic, age of mammals, 351. 
Centipedes, 153. 
Cephalopoda, 118. 
Cephalothorax, 124. 
Ceratodus, 223. 
Cercaria, 65, 66. 
Cerebellum, 309. 
Cerebrum, 308. 
Cetacea, 317. 

Chalk beds, formation of, 30. 
Chameleons, 255, 256. 
Chilopoda, 153, 198. 
Chimpanzee, 333. 
Chinch bug, 197. 



Chiroptera, 331. 

Chlorophyll in animals, 9. 

Chordata, 200, 201 ; classification of, 
202. 

Chromosomes, 20. 

Chrysalis, 179. 

Cicada, 17-year, 177 ; 13-year, 177. 

Cilia, 31. 

Circulation in animals, 363. 

Clams, 112. 

Class, 27. 

Classification of animals, 24 ; of cats, 
28. 

Clitellum, 75. 

Cloaca, 38. 

Coal, 7. 

Cobra, 251. 

Cochineal, 196. 

Cockroaches, 173. 

Cocoon, 179, 186. 

Codfish, 220, 227 ; rate of increase, 
353. 

Ccelenterata, 45 ; classification of, 63 ; 
economic importance of, 62. 

Ccelome of earthworm, 76 ; of star- 
fish, 93. 

Collar cells, 39. 

Colorado potato beetle, 187. 

Commensalism, 141. 

Congo snake, 239. 

Conjugation, 31. 

Contractile vacuole, 14. 

Copperhead, 252. 

Coral, 57 ; reefs, 58 ; red, 59 ; polyps, 
54, 57, 58, 59 ; fossil, 344. 

Cormorant, 282. 

Cotton boll weevil, 188, 190. 

Cowbird, 293. 

Crabs, hermit, 137; rock, 138; 
spider, 140 ; fiddler, 140. 

Crake, Carolina, 284. 

Cranes, 284 ; whooping, 284 ; sand- 
hill, 284. 

Crayfish, 124 ; appendages of, 125 
gills of, 126; locomotion of, 127 
alimentary canal, 128 ; food, 128 
circulation, 129 ; nervous system 
130 ; senses, 131 ; respiration, 131 
reproduction, 132 ; regeneration of 
lost parts, 132 ; molting, 133 ; eco- 
nomic importance, 134. 

Crickets, 171. 



INDEX 



383 



Crinoids., 99, 345. 

Crocodiles, 263. 

Crop, 85, 273. 

Crustacea, 124 ; economic importance 

of, 142 ; characteristics of, 143 ; 

classification of, 197. 
Ctenophora, 60. 
Cud, chewing, 321. 
Culex, 185. 
Curculio, 188. 
Cuttlefish, 119. 
Cuvier, 378. 
Cyclops, 135. 
Cyst, 66. 
Cytoplasm, 12. 

Diaphragm, 307. 

Darwin, Charles, 378, 379 ; Erasmus, 
379. 

Digestion of animals, 361. 

Dimorphism, 60. 

Diplopoda, 153, 198. 

Dispersal of animals, 367, 368. 

Distribution, geographical, of animals, 
365 ; questions of, 365 ; as reveal- 
ing history of the earth, 373. 

Doves, 287. 

Dragon flies, 173. 

Duckbill, 311. 

Ducks, 283 ; mallard, 283 ; canvas- 
back, 283 ; eider, 283. 

Dugongs, 318. 

Eagles, 285, 286. 

Earthworm, 75 ; external features, 75 ; 

diagram of body, 76 ; structure of 

walls, 77 ; setae, 78 ; movement, 77 ; 

digestive system, 79 ; digestion, 80, 

358 ; circulation, 80 ; nerves, 82 ; 

senses, 82 ; food, 83 ; life history, 

84 ; habits, 84. 
Echinodermata, 89 ; classification of, 

102 ; economic importance of, 101 ; 

characteristics of, 101 ; digestion of, 

360. 
Ectoderm of Hydra, 47. 
Ectoplasm of Amoeba, 14. 
Edentates, 314. 

Eels, 222 ; electric, 223 ; mud, 238. 
Egg cells, 19. 
Egg, defined, 19. 
Egg-laying mammals, 311. 



Eggs of mosquitoes, 185. 

Elephants, 322. 

Endoderm of Hydra, 47. 

Endoplasm of Amoeba, 14. 

Ephyra of Aurelia, 54. 

Epiglottis, 307. 

Epithelium cell, 10 ; of earthworm, 77. 

Eras of the earth, 341. 

Esophageal collar of earthworm, 82. 

Eyes of locust, 157; of perch, 208. 

Excretion of animals, 362. 

Family, 26. 

Faunal areas, 371. 

Fauna of a region, 370. 

Feathers, 270, 271, 292 ; thread, 270 ; 
contour, 270 ; down, 270. 

Feather stars, 99. 

Ferae, 323. 

Figs, cross fertilization of, 196. 

Fins of a fish, 209. 

Fish, how it swims, 214. 

Fishes, 204, 208 ; bony, 218; anadro- 
mous, 220 ; flying, 221 ; blind, 222 ; 
lung, 223 ; characteristics of, 224 ; 
adaptations of, 225 ; economic 
value of, 226 ; classification of, 228 ; 
fossil, 344. 

Fisheries, cod, 227; herring, 227; 
salmon, 227 ; mackerel, 227. 

Fission of Amoeba, 16. 

Flagellum, 37. 

Flatworms, 64. 

Flies, 183 ; horse, 186. 

Flukeworms, 65. 

Food vacuoles of Amoeba, 15. 

Foraminifera, 30. 

Fossils defined, 341. 

Frogs, green, 229 ; eyes, 230 ; ears, 
230 ; respiration of. 230 ; locomo- 
tion of, 231 ; alimentary canal, 232 ; 
circulation of, 232; food, 233; 
reproduction of, 233 ; habits of, 
235 ; wood, 240. 

Function, relation of, to structure, 22. 

Ganoids, 217, 223. 
Gastric follicles, 362. 
Gasteropoda, 114. 
Genus explained, 25. 
Geographical distribution of animals, 
366. 



384 



INDEX 



Gesner, Conrad von, 375. 

Gila monster, 259, 354. 

Gill scoop, 126. 

Gills of mussel, 106; of crayfish, 126; 
of fish, 210. 

Glass rope sponge, 42. 

Globigerina, 30. 

Glottis, 307. 

Gnats, 186. 

Goethe, 379. 

Goose, 283: Canada, 284. 

Gorilla, 334. 

Grantia, 38; structure of, 38; respira- 
tion of, 40; reproduction of, 44. 

Grasshoppers, Carolina, 155; dis- 
tribution, 155; eyes, 157; mouth 
parts, 158; food, 160; respiration, 
161; circulation, 162; reproduction, 
163; economic importance of, 164; 
American, 170; sounds of, 171. 

Greeks, 374. 

Grew, 376. 

Grouse, ruffed, 287. 

Growth of animals, 21. 

Gulls, 282. 

Haeckel, Ernst, 379. 

Haemoglobin of earthworm's blood, 

81. 
Hagfishes, 206, 207. 
Hair, 302. 

Hare, American, 357. 
Harvest fly, dog-day, 177. 
Harvey, William, 377. 
Hawks, 285. 
Helix, 116. 
Hell bender, 238. 
Heller, 377. 
Hermit crab, 61. 
Herring, 219, 22/. 
Hexapoda, 170. 
Hinge ligament, 103. 
Hippopotamus, 320. 
Honey dew, 190. 
Hood, 370. 
Hornbill, 294, 
Horned toad, 257, 352. 
Hornets, 191. 
Horn fly, 367. 

Horse, 8, 320; fossils of 320. 
Horsefly, 186. 
House fly, 186. 



Hydra, 46, 48; locomotion of, 46; 
structure of, 47 ; means of protec- 
tion, 48; digestion, excretion, and 
reproduction, 49; mode of ingestion, 
360; mode of digestion, 361. 

Hydractinia, 61. 

Hydrogen, 7. 

Hydrozoa, 50. 

Hyla versicolor, 241. 

Humming bird, ruby-throated, 288, 
290. 

Hunter, 377. 

Huxley, Thomas H., 379. 

Incisors, 304. 

Ingestion, 360. 

Insectivora, 329. 

Insects, number of, 9; class, 155; ad- 
aptations of, 194; economic impor- 
tance of, 195; characteristics of, 
197; classification of, 198; fossil, 
345. 

Invertebrates, 200, 201. 

Janssen, Hans and Zacharias, 375. 
Jelly fishes, 52. 

Kallima, 356. 

Kangaroo, 313; great gray, 313; rat, 

313; milk glands of, 313. 
Karyokinesis, 20. 
Katydids, 171, 355. 

Ladybird beetles, 188. 

Lamarck, 377. 

Lampreys, 205, 206; sea, 206; fresh- 
water, 206. 

Lampshells, 72, 344. 

Lancelet, 204, 205. 

Larva, 180, 186. 

Larynx, 307. 

Leaf butterfly, 356. 

Leeches, 85. 

Leeuwenhoek, 376. 

Lemurs, 333. 

Leptocardii, 204. 

Life, 8, 9; processes in animals, 
360. 

Limneea, 115, 116. 

Lingual ribbon, 115. 

Linnaeus, 376. 

Lion, 325. 



INDEX 



385 



Liver, 362. 

Lizards, 246, 254; six-lined, 246; eyes 
of, 246; ears and nostrils of, 247; 
mouth and teeth of, 247; locomo- 
tion of, 247; food of, 247; scales of, 
243; digestive system of, 248; blue- 
tailed, 254; alligator, 255; charac- 
teristics of, 259. 

Llamas, 322. 

Lobsters, 134. 

Locusts, 155, 164. 

Loons, 280. 

Lung fishes, 223, 224. 

Macaws, 291. 

Machinelike animal, 23. 

Mackerel, 218, 227. 

Macrocheira, 140. 

Madagascar, 368. 

Madreporite, 90. 

Maggot, 186. 

Malaria, 185. 

Malpighi, 375. 

Malpighian vessels, 363. 

Mammals, 302; characteristics of, 
334, 338; adaptations of, 335, 336, 
337; classification of, 338. 

Mammoth, 352. 

Man, 334, 350. 

Manatee, 319. 

Mandibles, 158. 

Mantes, 173. 

Mantle, 105. 

Marsipobranchii, 205. 

Marsupialia, 313. 

Mastodon, 352. 

Maxillae, 158. 

Maxillipeds, 125. 

May beetles, 187. 

Measuring worm, 356. 

Medulla oblongata, 309. 

Medusae, 52. 

Megalops, 139. 

Mesoderm, 90. 

Mesogloea, 47. 

Mesothorax, 158. 

Mesozoic, 347. 

Metamorphosis, incomplete, 164; 
complete, 168. 

Metathorax, 158. 

Metridium, 55. 

Midges, 186. 



Millipedes, 153. 

Mimicry, protective, 357. 

Minerals in animals and plants, 7. 8. 

Mites, 145. 

Mitosis, 20. 

Mocking bird, 291, 293. 

Moles, 330. 

Mollusca, 103; economic importance 
of, 122; classification of, 123; char- 
acteristics of, 121. 

Mollusks, digestion of, 361; fossil, 
345. 

Monarch butterfly, 358. 

Monotremata, 311. 

Mosquitoes, 35, 184, 185, 186. 

Moths, 178, 179; tomato, 180: cod- 
ling, 181; cotton, 181; polyphe- 
mus, 182; peach-tree borer, 182. 

Mussel, 103; structure of shell, 103; 
respiration of, 106; locomotion of, 
107; alimentary canal, 108; circu- 
lation of, 109; reproduction of 
110. 

Mya, 112. 

Nacre, 111. 
Nautilus, pearly, 120. 
Necturus. 238. 
Nemathelminthes, 64. 
Xephridia. 82. 
Nests, edible, 294. 
Newts, 240. 
Night-hawks, 289. 
Nomenclature, binomial, 376. 
Notochord, 200. 
Nucleus, 12. 
Nudibranchs, 117. 
Nymphs, 163. 

Octopus, 119. 

Olfactory lobes. 309. 

Oosperm explained, 21. 

Operculum, 210. 

Opossum, 314. 

Oral surface, 90. 

Orang-outang, 333. 

Order explained, 27. 

Organ defined, 22; functions of, 22. 

Orioles, Baltimore, 291, 294. 

Orthoceras, 345. 

Osculum of Grantia, 37. 

Ostriches, 279, 280. 



386 



INDEX 



Owen, 379. 

Owls, 285 ; barn, 285 ; screech, 285 ; 

burrowing, 285. 
Oysters, 113. 
Oxygen, 7. 

Palaeozoic, age of invertebrates, 343. 

Pancreas, 362. 

Paramecium, 30, 31, 358; reproduc- 
tion and conjugation of, 31. 

Parrots, 290 ; Carolina, 290. 

Partridges, 287. 

Pearl oyster, 114. 

Pearls, 111. 

Pelecypoda, 112. 

Pelican, white, 283. 

Penguins, 280. 

Perch, 208; respiration of, 211; ali- 
mentary canal of, 211 ; circulation 
of, 212 ; plan of structure, 213 ; re- 
production of, 214. 

Perching birds, 291. 

Pericardium, 109. 

Petrel, stormy, 282. 

Phrynosoma, 257. 

Physa, 115, 116. 

Pigeons, 287. 

Pike, gar, 217, 218. 

Plant lice, 190. 

Plantigrade animals, 324. 

Plastron, 262. 

Pliny, 374. 

Plum curculio, 188. 

Pluteus, 100. 

Pompano, 221. 

Porcupine, 327. 

Porifera, 36 ; classification of, 44. 

Pouched mammals, 313. 

Prairie dogs, 328. 

Prawns, 137. 

Primates, 333. 

Prostomium of earthworm, 75. 

Protective resemblances, 355. 

Protoplasm described, 11 ; work of, 
12. 

Protozoa, 29 ; characteristics of, 33 ; 
economic importance of, 34 ; classi- 
fication of, 35 ; secretion and diges- 
tion of, 362 ; circulation of, 363 ; 
reproduction of, 364. 

Psalterium, 321. 

Pseudopodia, 14. 



Pupse of mosquito, 186. 
Pyloric cseca, 91. 

Quahog, 112. • 
Quails, 286, 287. 
Quill, 269, 271. 

Rabbit, gray, 302 ; white, 357 ; diges- 
tion of, 306 ; hair of, 302 ; eyes of, 
303 ; ears and nostrils of, 303 ; 
teeth of, 304 ; food of, 304 ; loco- 
motion of, 305 ; digestive system 
of, 306 ; respiration of, 307 ; circu- 
lation of, 309 ; economic import- 
ance of, 309. 

Raccoon, 324. 

Pachis, 271. 

Radial symmetry, 89. 

Ray, 216 ; electrical, 217 ; feting, 217. 

Pay, John, 376. 

Redia, 65. 

Regeneration of lost parts in an earth- 
worm, 83 ; in echinoderms, 100 ; in 
crustaceans, 141. 

Reptiles, fossil, 347. 

Reptilia, 246 ; characteristics of, 265 ; 
adaptations of, 265, 266 ; classifica- 
tion of, 267. 

Reproduction in animals, 364. 

Resemblances, protective, 355 ; ag- 
gressive, 357. 

Respiratory cseca, 363. 

Reticulum, 321. 

Rhinoceros, 320 ; Indian, 320 ; black, 
320. 

Rodentia, 327. 

Rotifer, 70, 71. 

Roundworms, 64, 68, 69. 

Rumen, 321. 

Ruminants, 321 ; stomach of, 321 ; 
cud of, 321. 

Salamanders, 239 ; spotted, 239. 
Salmon, 225, 227. 
Sand-dollars, 97. 
San Jose scale insect, 178. 
Sapsucker, yellow-bellied, 288. 
Sawfishes, 215, 217. 
Scale insects, 178, 196. 
Scales of a fish, 208. 
Schwann, 378. 
Schleiden, 378. 



INDEX 



387 



Scorpions, 144. 

Scyphozoa, 52. 

Sea anemones, 54, 55, 360. 

Sea cucumbers, 97, 98. 

Sea lilies, 99, 345. 

Seal, fur, 325. 

Seashells, 118. 

Sea squirts, 203. 

Sea urchins, 95, 96, 97. 

Sea walnuts, 60. 

Sea worms, 86. 

Secretion of animals, 361. 

.Setae of earthworms, 78. 

Sexual reproduction, 364. 

Sharks, 215 ; hammer-headed, 215, 
216 ; great basking, 216 ; mouth of, 
216 ; gills of, 216. 

Sheepshead, 221. 

Shellac, 196. 

Ship worm, 114. 

Shrew, 329. 

Shrimp, 137. 

Siebold, 379. 

Siphon of mussel, 105. 

Siphuncle, 120. 

Siren, 238. 

Sirenia, 319. 

Skates, 216. 

Skeleton, internal, 204 ; external, 204. 

Sloth, 315. 

Slugs, 116, 117. 

Snails, 115. 

Snakes, garter, 249 ; cobra, 251 ; cop- 
perhead, 252 ; water-moccasin, 252 ; 
rattlesnake, 252 ; harlequin, 254 ; 
characteristics of, 254. 

Snapper, red, 221. 

Sowbug, 141. 

Sparrow, English, 268, 365 ; plumage 
of, 269 ; wings, 271 ; legs and feet, 
perching, 272 ; digestion of, 273 ; 
272 ; alimentary canal, 273 ; circu- 
lation of, 274 ; respiration of, 275 ; 
senses of, 275 ; nervous system of, 
275; life history of , 276 ; food, 277 ; 
economic importance of, 277. 

Species defined, 25 ; affected by dis- 
tribution of animals, 371 ; extermi- 
nation of, 372 ; formation of, 372. 

Spermaceti, 317. 

Spicules, 39. 

Spiders, 146 ; web of, 149 ; balloon- 



ing, 150 ; cobweb, 150 ; orb, 150 ; 
trapdoor, 151. 

Spinnarets, 148. 

Sponges, 36 ; skeleton of, 41 ; sili- 
ceous, 42 ; commercial, 43 ; eco- 
nomic importance of, 44 ; classifi- 
cation of, 44 ; mode of digestion, 
361. 

Spontaneous generation, 18. 

Spoonbill, 217. 

Squid, 118. 

Starch, 7. 

Starfish, 89; body walls of , 90 ; skele- 
ton of, 90 ; food of, 91 ; locomotion 
of, 92 ; nervous system of, 93 ; life 
history of, 93 ; ccelome of, 93. 

St. Hilaire, Geoffrey, 378. 

Stingaree, 216. 

Stinging thread cells, 47. 

Struggle for existence, 353. 

Sturgeons, 217 ; roe of, 218. 

Survival of the fittest, 354. 

Swammerdam, 376. 

Swifts, 288, 294 ; chimney, 290. 

Syrphus flies, 359. 

Tailor birds, 295. 

Tapeworms, kinds of, 66 ; life history 

of, 67 ; mode of ingestion, 360. 
Tapir, 320. 
Tarantula, 151. 
Teeth of rodents, 327. 
Tentacles, 46, 47, 49. 
Teredo, 114. 
Terns, 282. 
Testudinidae, 259. 
Thorax, 307. 
Thrush, Wilson's, 291. 
Tick, 34 ; dog, 146 ; cattle, 145. 
Tiger, 325. 
Toad, common, 235, 352 ; molting of, 

236 ; hibernation of, 237 ; Surinam, 

237 ; tree, 240 ; horned, 257, 354. 
Toothless mammals, 314. 
Tortoise, 259. 

Tree frogs, 240, 243. 
Treviranus, 379. 
Trichinella spiralis, 69. 
Trilobites, 343. 
Trout, 221. 
Tube feet, 90. 
Tunicates, 203. 



388 



INDEX 



Turtles, 259; leather back, 260; 
green, 260 ; painted, 260 ; snap- 
ping, 261 ; soft-shelled, 261 ; go- 
pher, 261 ; characteristics of, 262. 

Umbo, 103. 
Ungulata, 319. 
Urochorda, 203. 

Vane, 271. 
Venus clam, 112. 
Venus's basket sponge, 42. 
Vertebrates, 200, 201, 204; mode of 

digestion of, 361. 
Vesal, 379. 

Viceroy butterfly, 358. 
Vorticella, 32. 

Walking sticks, 355. 
Wallace, A. R., 379. 
Walrus, 326. 



Wasps, 191, 192; mud-daubers, 192; 
polistes, 191, 192; vespa, 192. 

Water vascular system, 92. 

Weaver birds, 294. 

Weismann, 379. 

Whales, 317 ; whalebone, 317 ; bow- 
head, 318; razor-back, 318; sul- 
phur bottom, 318 ; sperm, 317. 

Whippoorwills, 288. 

White, Gilbert, 377. 

Winged mammals, 331. 

Wolff, 379. 

Woodcock, 284. 

Woodpecker, 287 ; red-headed, 287. 

Wotten, 379. 

Yellow fever, 185. 

Zeuglodon, 352. 

Zoea, 139. 

Zooids, 51. 

Zoology, definition and extent of, 9. 



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